SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE. —$_——————— 239 OBSERVATIONS ON TERRESTRIAL MAGNETISM AND ON THE DEVIATIONS OF THE COMPASSES OF THE UNITED STATES IRON CLAD MONADNOCK DURING HER CRUISE FROM PHILADELPHIA TO SAN FRANCISCO, IN 1865 AND 1866. BY WM. HARKNESS, M.D., PROFESSIR OF MATHEMATICS, UNITED STATES NAVY. [ACCEPTED FOR PUBLICATION, SEPTEMBER, 1871.] INTRODUCTORY NOTE. THis paper was originally an official report presented to the Navy Department by Professor Harkness; but, as that department made no use of it, the National Academy of Sciences, in August, 1867, passed a resolution asking for the manuscript. This request was complied with; and, an abstract of the paper having been read to the Academy in April, 1869, it was referred to a commission consisting of the President of the Academy, Professors J. H. C. Coffin, and F. Rogers, in accordance with whose recommendation it is now published by the Smithsonian Institution. dJoOsEPH HENRY, Secretary S. I. —=x COLUINS, PRINTER, PHILADELPHIA, TABLE OF CONTENTS. SECTION f. INTRODUCTION. Introductory remarks. . ; ° . r Plan of observation - “ - 2 Instruments employed . 4 4 2 : ° SECTION IT. DESCRIPTIONS OF STATIONS. Philadelphia =. ° . ° 5 = Gosport. : ° . 4 5 ; 5 St. Thomas : 4 4 5 < : . Isle Royal ° : é 5 . - . Ceara . A 5 : : : c Pernambuco 3 5 ' : - c Bahia. 5 : : “ : 5 < Rio Janeiro : 2 . : 5 : 6 Monte Video . . 5 5 A E ; Sandy Point . - : ° : - Valparaiso ¢ : ° . ° < Callao . i cC : - : S Payta . : c ° 5 - ‘ = Panama. 5 A = . C Acapulco : 5 5 - : E i Magdalena Bay. Z : s Fi San Francisco . A ; a : _ SECTION III. ASTRONOMICAL OBSERVATIONS, General remarks é : - c . Observations of the sun for intiinde ; : . . Observations of the sun for time Mode of determining true bearings : Observations of the sun for the ees of true fee Triangulation at Ceara . ; : : : a Table of observed latitudes : : . Errors of pocket chronometer, Bletcher No. 906 : ° Chronometer comparisons : : . True bearings of objects used as eeimull nee : ° b= DBNATADPMOAAIA oS —} a) 10 10 11 11 12 13 13 14 26 28 32 34 35 36 36 lV CONTENTS. SECTION IV. OBSERVATIONS ON TERRESTRIAL MAGNETISM. Deseription of the portable declinometer, D. 22 2 : Description of the transit theodolite General remarks on the methods of using the fneienmenis Mode of determining absolute declinations Mode of making observations of vibrations Mode of making observations of deflections Mode of calculating horizontal force Determination of constants peculiar to the aamintle SecBmamaion D. 22 Temperature coefficients of magnets Value of magnet scales Moment of inertia of the magnet, . 32 The constant P. Magnetic moment of the magnet C. 32. Mode of making observations of inclination Mode of computing the vertical and total force . Abstract of observations for magnetic declination, inclination, ond fore Final values of the magnetic elements at each station . Observations of magnetic declination Observations of magnetic inclination Horizontal intensity. Observations of Hinting Horizontal intensity. Observations of deflections SECTION V. OBSERVATIONS ON THE MAGNETISM OF THE SHIP. Description of the Monadnock . Positions of the compasses Mode of swinging the ship. Corrections peculiar to the After Binnacle and After Ritchie Compasnas Officers who observed the compasses Mode of measuring magnetic force on board shih Mathematical theory of the deviations of the compass . Correction of observed deviations for constant errors Observations for determining the deviations of the Admiralty Standard Connpace Observations for determining the deviations of the After Binnacle Compass Observations for determining the deviations of the After Ritchie Compass Observations for determining the deviations of the After Azimuth Compass Observations for determining the deviations of the Forward Alidade Compass Observations for determining the deviations of the Forward Binnacle Compass Observations for determining the deviations of the Forward Ritchie Compass . Mode of computing the coefficients 4,, B,, C,, D,, EL, . Values of these coefficients for each compass at each station Probable errors of the values of the coefficients A,, B,, C,, D,, £, a a ae s, - and AQ for each compassn n n Values of the coefficients 9[, 8, CG, 5, G, for “ak ae at each station Computation of the constants A,, Table showing the aallnes af ihe cometonts A= NS, z av ef, Q AQ ®, and G, ry 9i, idan for each compass : a 0 2 2 6 < 2 101 110 119 120 120 121 122 122 123 129 133 140 147 154 160 167 174 181 182 184 185 191 193 CONTENTS. Computation of the coefficients 9, B, C, D, G, for each compass at each station, from the constants, A,, °, P AP f Q aQ D, and &. Rhea, Ne (Agee Comparison of the coefficients thus computed with those found directly from the observations at each station Resulting probable errors Does the theory accurately represent ite Eee enter ve tian? Tables atta the most important features of the deviations of each compass aang the cruise . Hard and soft iron oe Magnetic moment of magnets used fort eaeerie poneeael ae on bead ine Observations for absolute force at the Admiralty Standard Compass Observations for absolute force at the After Azimuth Compass Values of Values of g,h, k, R a AR, for the Ravairait disadard and ‘After Asinintl Sclaumneced Values of a, b, e, and d, for the Admiralty Standard and After Azimuth Compasses . General equations for the determination of the deviations of the Admiralty Standard Gautaies General equations for the determination of the deviations of the After Azimuth Compass Variations of the hard iron force, during the cruise, at the Admiralty Standard and After Azimuth Compasses : : ; : ; : : : Computation of the coefficients A,, B,, C,, D,, Z,, for each compass, at places where the deviations were observed on less than thirty-two points Recapitulation of results Final conclusions PAGE REPORT ON MAGNETIC OBSERVATIONS. SECTION I. END RO DUC PRON On the fifth of October, 1865, I was ordered to the U. 8S. Iron-clad Monad- nock! for the purpose of making observations on the action of her compasses during the cruise which she was about to undertake from Philadelphia to San Francisco, by way of the Straits of Magellan. She was then fitting out at the Philadelphia Navy Yard, and the work on her was so far advanced that it was expected she would sail in about two weeks. As the department had not previ- ously intimated its intention of assigning me to this duty, and as everything relating to the number and kind of observations to be made, and the instru- ments required, was left entirely to my own discretion, it will be seen that the time available for making plans and collecting the necessary apparatus was very limited. The plan of observation ultimately adopted was that at every port in which we remained for more than twenty-four hours the following operations should be gone through with. Ist. The ship should be swung, and as her head pointed successively to each of the thirty-two true magnetic points, the reading of every compass on board should be recorded for each point. 2d. That at such of the compasses as were so situated as to render it possible, the horizontal force and inclination should be determined. 3d. The position of the dividing line be- tween the north and south polarity should be traced on each turret. 4th. The magnetic declination, inclination, and horizontal force should be determined on shore. While at sea it was intended to observe the declination—and consequently the deviation—and horizontal force daily, by means of the standard compass; but this turned out to be impracticable, because the only place in the ship where it was possible to mount that instrument was on top of the after pilot-house; a situation ! The Monadnock is a double-turreted vessel of the monitor type. During the cruise in question, Lieutenant Commander Francis M. Bunce, U.S. N., was her captain, and she was attached to the squadron commanded by Commodore (now Rear-Admiral) John Rogers, U.S. N., at whose special request I was detailed by the Navy Department to make the observations which are the subject of this paper. 1 December, 1871. ( 1 ) 2 REPORT ON where no binnacle could be put, and where the compass was nearly on a level with the top of the smoke-stack. ‘Thus, while at sea, the position occupied by it was almost constantly enveloped in smoke and gas, rendering it absolutely necessary, whenever we left port, to dismount the instrument in order to preserve it from injury. Owing to the very short time at my disposal previous to sailing, there was great difficulty in providing proper instruments, but I succeeded in obtaining all that were absolutely necessary. ‘The following is a list of them: 1 Portable Declinometer and stand. 1 Five-inch Altitude and Azimuth Instrument. 1 Dip Circle, with two needles, each three and a half inches long. 1 Pair of eight-inch Bar Magnets. 1 Pair of eleven-inch Bar Magnets. 2 Admiralty Standard Compasses, with stands and deflectors. 1 Burt’s Solar Compass and stand. 1 Prismatic Sextant of six inches radius. 1 Mercurial Artificial Horizon. 1 Pocket Chronometer, Fletcher, No. 906. 1 Silver Comparing Watch. 2 Pocket Thermometers. 2 Pocket Compasses. 2 Magnetic Needles, not mounted, each 2.75 inches long, and 0.33 of an inch broad. 1 Fifty feet Chesterman’s Patent Tape Line. 1 Case of Drawing Instruments. 1 Gunter’s Scale, two feet long. The portable declinometer belonged to the U.S. Coast Survey, and was kindly lent by Prof. J. EK. Hilgard. The small unmounted magnetic needles were intended to be used for measuring the relative horizontal force on shore and at each of the compasses on board ship. For this purpose it was proposed to vibrate one of them on shore, and then taking it on board ship to the compass at which it was desired to measure the relative horizontal force, to remove the compass card from the centre-point, and putting the small needle in its place, vibrate it again. Unfortunately the small needles were not finished till just before we left Philadelphia, and there was no opportunity of trying them till after we were at sea, when, to my great regret, it was found that the jewels were so small that they would not fit on the centre-point of any compass on board, thus rendering them entirely useless. Under the circumstances, for horizontal force on board ship it was necessary to rely entirely upon measures made with the deflectors belonging to the Admiralty standard compasses—a method certainly not so convenient, and, owing to the constant swinging of the ship when at anchor, probably not so accurate as counting the vibrations of a small needle. oie The observations on terrestrial magnetism, and for latitude, time, and true bear- ings, were all made by myself and recorded by Mr, Corrin F. Smith, who was cap- tain’s clerk on the Monadnock, and acted as my assistant when I was observing. My best thanks are due to him for the efficient. manner in which he performed his duties, sometimes under circumstances of very considerable physical discomfort. MAGNETIC OBSERVATIONS. 3 The reductions and discussions in this report have been made by me, so that I am personally responsible, not only for the general plan of the work, but for every figure contained in it. All the results have been very carefully checked, and it is hoped no material error will be found in them; still, absolute accuracy is scarcely to be expected in any work involving so many figures, the more especially as much of it has been done during moments snatched from other and more pressing professional duties. The observations naturally divide themselves into three classes: 1st. Those relating to astronomy. 2d. ‘Those relating to terrestrial magnetism. 3d. Those relating to the magnetism of the ship. As that is the order in which they must necessarily be reduced, they will be so treated of in the subsequent sections of this report. SG WO Iles DESCRIPTIONS OF STATIONS. Un.ess otherwise stated, the assumed positions of light-houses, forts, ete., have been taken from the English Admiralty Charts, or from the English Admiralty List of Lights, the latest editions obtainable in 1865 being employed. The longi- tudes are counted from the meridian of Greenwich. The method used in testing a station for local attraction by means of fore and back sights with a compass, was as follows: The compass was set up at the station, and the bearing of a point distant one hundred yards, or more, was observed. Then the compass was transferred to that point, and the bearing of the station was observed. These two bearings should evidently differ from each other by 180°; if they did not, it was certain that local attraction existed at one or both of the points, and a new station was sought for. This process is almost certain to detect any strictly local magnetic attraction, but it will not suffice to demonstrate the existence of an abnormal state of the magnetic elements extending over a large territory. PHILADELPHIA, Pa. The magnetic observations were made at a spot-on the east bank of the Delaware river, about twenty feet from the water’s edge. It is nearly southeast from the U.S. Navy Yard, from which it is distant about three-quarters of amile. The soil is a dark—nearly black—earth, which appears to have been deposited by the river. The approximate position of the station was Lat. 39° 55'N. Mone lon OP w ead We Gosport, Va. ‘The magnetic observations were made on a white sandy beach, on the west bank of the Elizabeth river, about thirty feet from the water’s edge. From the place where the instruments stood, the flagstaff in the U.S. Navy Yard - bore due north by compass, and was distant about half a mile. Assuming the position of the flagstaff to be lat. 36° 49’ 32’ N., long. 5° 5™ 9°.8 W., as stated by the authorities at the Navy Yard, the positionse: of the spot occupied iby the instruments is approximately Lat. 36° 49 O’N. Wongs 8a 25" 92:3 Ws The ship was swung at the compass station in Hampton Roads, on November Ist, 1865, in the usual manner. Her position at the time was lat. 36° 58’ N. , long. 76° 20’ W. Joint XII on the after turret was 14. : inches to port. (4) MAGNETIC OBSERVATIONS. 5 Sr. Tuomas, West Indies. The ship was swung in this harbor, on November 18th, 1865, in the usual manner. Her position at the time was lat. 18° 19’ N., long. 64° 56’ W. Joint XII on the after turret was 14.4 inches to port. The observations on shore were made in Long Bay, at a spot about thirty feet from the water’s edge, on a gravelly beach, to the eastward of the town. From the place where the instruments stood the true bearing of Fort Cowell, at the en- trance to the harbor, is S. 34° 50’ W., and it is distant about one mile. Assuming the position of Fort Christian to be lat. 18° 20’ 27’ N., long. 4" 19™ 42°.7 W., then, according to the English Admiralty Chart, the position of the spot where the instruments were set up is (cat elo me Oe eo IN Longs <4" "19" 40°.6 W. Iste Roya, Salute Islands. An attempt was made to swing the ship here, on November 30th, 1865, in the usual manner, but it failed on account of the continual rain which shut off the view of the distant azimuth mark. The position of the ship at the time was lat. 5° 17’ N., long. 52° 83’ W. Joint XII on the after turret was 0.6 of an inch to starboard. The magnetic and astronomical observations on shore were made on the south- west side of the island, at a spot from which the corner made by the southeast and southwest faces of the government coal sheds bears N. 64° W. (true), and is distant one hundred and thirty-two feet. The place was examined carefully for local attraction by taking fore and back sights with a compass, but none could be detected. The position occupied by the instruments is in Lats 5d ne ie 20" Ne Tong. 3' - 30" 11.4 W. The latitude was determined from a single set of circummeridian altitudes of the sun observed by me, and the longitude was taken from the French chart. Ceara, Brazil. An attempt was made to swing the ship here, on December 19th, 1865, in the usual manner, but although a very favorable opportunity was chosen, she could only be made to turn through ten points. Her position at the time was lat. 3° 44’ S., long. 38° 34’ W. Joint XII on the after turret was 0.6 of an inch to starboard. The wind, current, and sea are so strong here that vessels at anchor in the roads always ride with their heads nearly in the same direction, never swinging more than about three points. At this place there is no harbor whatever, merely an open roadstead. A heavy surf is constantly running on the beach, and as there are almost no facilities for landing in small boats, getting the instruments on shore involved a good deal of trouble and some risk. However, I succeeded in landing them safely, and obtained a very good set of observations on the white sand beach at a spot about one hundred and fifty feet from the water’s edge, and from which the true bear- ing of the southeast corner of the custom-house on the wharf is N. 53°19’ W., and its distance two hundred feet. From the same spot the true bearing of 6 REPORT ON Point Macoripe Light-house is N. 75° 38’ E. The position occupied by the instruments is in ibag, 88 4ey BO" Ss. Long. 2" 34™ 6° W. The latitude was deduced from my own observations, and the longitude was taken from the list of geographical positions given in Raper’s Navigation. PernamBuco, Brazil. The ship was not swung in this port because there was not room to do it in the position where she took her coal, and as she only remained in the harbor twenty-four hours, there was not time to take up another position in order to swing. The magnetic and astronomical observations on shore were made on the white sand beach, at a spot from which the true bearing of the salient angle of the southeast bastion of Fort Brum is N. 15° 46’ W., and its distance four hundred and thirty feet. Assuming the position of the light-house, near to Fort Picao, to be lat. 8° 3’ 42” S., long. 2" 19™ 26°.8 W., as it is given in the English Admiralty List of Lights, edition of 1866, then, according to the English Admiralty Chart, the position occupied by the instruments is in ate eOy ouusolnS: Long. 2? 19™ 28°.2 W. Banta, Brazil. The ship was swung in this harbor, on December 30th, 1865, in the usual manner. Her position at the time was lat. 12° 59’S., long. 38° 31’ W. Joint XII on the after turret was 0.6 of an inch to starboard. The magnetic and astronomical observations of December 27th were made at a spot, one hundred and fifty feet from the water’s edge, situated in a cocoanut grove on the beach about half-way between Monserat Point and Fort Victoria. The soil is a coarse white sand. It was not possible to get any bearings which would define the exact position, but the above directions are sufficient to enable any one to find the place very nearly. ' Assuming the position of Fort St. Antonio Light to be lat. 13° 0’ 55” S., long. 2 34™ 6°.9 W., then, according to the English Admiralty Chart, the position occu- pied by the instruments is in Tat 22 yas fool 1S: Long. 2" 34™ 08.5 W. Rio JAnzIRO, Brazil. The ship was swung in this harbor, on January 10th, 1866, in the usual manner; but, owing to a strong wind which was blowing at the time, it was not possible to get her through more than seventeen points. Her position was lat. 22° 54’ §., long. 48° 9’ W. Joint XII on the after turret was 0.8 of an inch to port. During the whole week we were at Rio there was not one clear day. Conse- quently it was extremely difficult to make astronomical observations, and it was only by patiently watching for the sun and seizing the opportunities when it was MAGNIKETIC OBSERVATIONS. qi momentarily visible through breaks in the clouds, that the few sights necessary in order to complete the magnetic observations were obtained. With a single exception, all the magnetic and astronomical observations were made at a spot from which the true bearing of the entrance on the north face of Fort Caraguata (erroneously spelled Gravata on the English charts) is 8. 70° W., and its distance fifty-five feet. There were no guns in the fort at the time. The surrounding country is very hilly, the bare, coarse, granite rocks cropping out every- where from the hill-sides, but in the more level places they are thinly covered with earth. Assuming the position of Fort Villegagnon to be lat. 22° 54’ 42’ S., long. 2» 52" 36°.0 W., then, according to the English Admiralty Chart, the position occupied by the instruments is in Lat. 22° 54 35'S. Long. 2" 52™ 30°.7 W. The exception referred to above is some observations of the sun for time, made on January 9th. They were-got on Rat Island, the spot where naval officers usually go to rate their chronometers when lying in this harbor. Assuming the position of Fort Villegagnon as above, then, according to the English Admiralty Chart, the position of Rat Island is Lat. 22° 53’ 45”S8. Long. 2° 52" 37°.9 W. Monte Vivx0, Uruguay. The ship was swung in this harbor, on January 24th, 1866, in the usual manner. We first attempted to get her around about 1 P. M., but owing to the force of the wind and tide we only obtained ten points, viz., those from E. by S. toS.8.W. Just at sunset we tried it again, and succeeded in getting the remainder of the circle. It was nearly dark when we finished, but as the dis- tant object used for an azimuth mark shone plainly against the sky, there was suf- ficient light to see pretty distinctly when it was in range with the sights of the compass. | The readings of part of the circle on the After Ritchie compass were lost, owing to the failure of daylight and delay in procuring a lantern. The officer who usually read the After Azimuth compass was on shore at the time, and the duty of making the observations at that instrument was assigned to another, but it turned out that he did not understand how to read an azimuth compass, and his observations were worthless. While we were lying at Monte Video the tide was very irregular. Most of the time the ship only swung to it about 90°, but two or three times she swung 180°. At the time we swung her to obtain the deviation of the compasses her position was lat. 34° 55’ S., long. 56° 13’ W., and joint XII on the after turret was 4.5 inches to port. The greater part of the magnetic observations on shore were made on January 18th, at a station on the ground occupied by Tomkinson’s slaughtering establishment. The instruments were set up at a spot where there are four large umbu trees stand- ing inaline. The exact position may be recovered by means of the following true bearings. The corner made by the south and west sides of the dwelling-house 8 REPORT ON bears N. 39° E., and is distant about one hundred feet. ‘The light-house on the Mount, on the west side of the harbor, bears N. 59° 0’ W. ‘The water’s edge is distant from the station about four hundred feet. The soil isa thin stratum of very poor earth, covering a greenish-colored slaty rock, which crops out in many places. Assuming the position of the light-house on the Mount to be lat. 34° 53’ 15” S., long. 3" 44" 59°.0 W., then, according to the English Admiralty Charts, the position occupied by the instruments is in’ Ibe BH BBY ROP S. Long. 3" 44™ 55°.8 W. As a check, some magnetic observations were made, on January 19th, at a station from which the true bearing of the light-house on the Mount is N. 89° 41’ W., and the true bearing of the light on the Cathedral is $. 17° 42’ W. Assuming the position of the light-house to be as stated above, and the light on the cathedral to be in lat. 34° 54’ 20’ S., long. 3" 44™ 50°.0 W., as given in the English Admiralty List of Lights in South America, edition of 1865, the geographical position of this station was at. 34° 53’ 16’S. Long. 3" 44™ 485.3 W. It will be observed that the difference of longitude between the lights on the Mount and on the cathedral, as deduced from the Admiralty List cited above, cannot be made to agree with the positions given on the English Admiralty Chart. On January 24th some observations for time were made on Rat Island. Assum- ing the position of the light-house on the Mount to be as stated above, then, accord-— ing to the English Admiralty Chart, the position of the station on Rat Island was Lat. 34° 53’ 18’S. Long. 3° 44" 525.9 W.- Sanpy Point, Straits ef Magellan. The ship was swung in this harbor, on February 10th, 1866, in the usual manner. Her position at the time was lat. 53° 11’ S., long. 70° 55’ W. Joint XII on the after turret was 4.5 inches to port. While we were lying here the ship was perfectly free to swing to the tide, but she generally turned through an arc of only about ninety degrees, namely, from W.N.W. to N.N.E. The observations on shore were made in the meadow, between the settlement and the beach, at a spot from which the true bearing of the flagstaff was N. 47° 8’ W., and its distance about eight hundred feet. The soil is sandy, and there is no rock anywhere near. The place was examined for local attraction by taking fore and back sights with a compass, but nothing of the kind could be detected. Assuming the position of the flagstaff to be lat. 58° 10’ 15’’S., long. 4" 43™ 36°.0 W., as given on the English Admiralty Chart, edition of 1861, the position occupied by the instruments is in Lat. 53° 10’ 20"S. Long. 4° 43" 355.3 W. MAGNETIC OBSERVATIONS. 9 VALPArAIso, Chile. The ship was swung in this harbor, on April 4th, 1866, in the usual manner. Her position at the time was lat. 33° 2’ S., long. 71° 38’ W. Joint XII on the after turret was 4.25 inches to port. While we were lying at Valparaiso the ship was perfectly free to swing to the tide, and she turned in all directions. The observations taken on shore March 2d were made on the south end of the white sand beach at the Estero de Quilpue, at a spot about two hundred and fifty feet from the rocks. Assuming the position of Fort San Antonio to be lat. 33° 1’ 53” §., long. 4" 46™ 46°.0 W., then, according to the English Admiralty Chart, the position of this station was approximately Lat. 33° 145. Long. 4° 467 31° W. The observations of March 19th, and all taken subsequently to that date, were made at a spot distant about six hundred and fifty feet, nearly true north, from the most northern of the custom-houses. The instruments were set up, near to the water’s edge, on the public road which here runs along under a high bank of rock. The true bearing of the flagstaff at Fort San Antonio, on the top of the hill, was S. 31° 45’ W., and its estimated distance was seven hundred feet. Assuming the posi- tion of the fort to be as stated above, the position occupied by the instruments is in hath) dao) RATES, Long. 4° 46™ 45°.7 W. Both this station and that of March 2d were carefully tested for local attraction by taking fore and back sights with a compass, but none could be detected. In adopting 4" 46™ 46°.0 as the longitude of Fort San Antonio, I have followed Raper, but this value is doubtless too large. Capt. Jas. M. Gilliss, U.S. N., from a series of occultations and moon culminations, observed during the years 1850-51-52, determined the longitude of the Observatory on the hill of Santa Lucia, in Santiago, to be 4 42™ 33°.8. Dr. Moesta, from subsequent observations up to the year 1862, corrected this value to 4" 42" 33°.0. Capt. Gilliss, by means of the electric tele- graph, found the difference of longitude between the Observatory at Santiago and Mr. Mouatt’s Observatory at Valparaiso to be 3™ 56°.5. Hence, adopting Dr. Moesta’s value of the longitude of Santiago, we have 4h 46™ 29°.5 W. as the longitude of Mr. Mouatt’s Observatory; but I have been unable to find any description of its position, and consequently cannot refer this longitude to Fort San Antonio. Findlay, in his “ Directory to the South Pacific Ocean,” edition of 1863, gives for the longitude of Fort San Antonio 4" 46™ 28°.8, and quotes Dr. Moesta as the authority. The Connaissance des Temps, for the year 1868, on the same authority- gives 4" 46™ 27°.5 for the same position. Which of the two values is nearest cor- rect I am unable to say. Caxiao, Peru. The ship was swung in this harbor, on April 29th, 1866, in the usual manner. Her position at the time was lat. 12° 3’ S., long. 77° 14’ W. Joint 2 December, 1871. 10 REPORT ON XII on the after turret was 5.5 inches to port. While we were lying at Callao the ship was perfectly free to swing to the tide, but the wind and current were so strong that she did not do so, but always lay with her head pointing in a southerly direction. The observations taken on shore, April 26th, were made on the northeast side of San Lorenzo Island, about two and a half miles southeast of the light-house. The island is a mass of hills, rising to an elevation of more than a thousand feet, com- posed of loose friable rock which seems to be of volcanic origin, and which is con- stantly disintegrating into a fine yellow sand. ‘The place selected for making the observations is at the foot of a gorge where there is a beach, about a quarter of a mile long, of the yellow sand mentioned above. On the beach stand a number of fishermen’s huts, and a few steps back, at the foot of the gorge, stands a large, square, two-story house. The spot where the instruments stood is on the southeast end of the beach, a little beyond the fishermen’s huts, and just above high-water mark. Assuming the position of the light-house to be lat. 12° 4’ 0’ S., long. 5" 9" 18°.0 W., the position occupied by the instruments is in Lat. 12° 5° 14'S. Monsey nO menounos VE The place was carefully tested for local attraction by taking fore and back sights with a compass, but none could be detected. Payta, Peru. We remained in this port only from 2" 30" P.M. of May 6th, 1866, till 6" P. M. of May 7th, and there was neither time nor opportunity to swing the ship. However, a complete set of magnetic observations were made on shore at a station on the beach four-tenths of a mile northwest of the large iron building which stands just back from the mole, and is used by the government as a custom- house, ete. As nearly as could be determined from angles carefully measured, and plotted on the English Admiralty Chart, this station is identical with the one occupied by the officers of H. B. M. surveying vessel “Beagle,” in the year 1836, when making their observations for determining the position of Payta. According to their determinations it is in Mat.) 6° 536/88: Long. 5° 24™ 22°.0 W., the longitude depending upon the position of the northeast bastion at Panama, New Granada, which is taken to be 5" 18™ 4°.6 W. The instruments were set up, just above high-water mark, on the gray sand beach, about fifty feet back from which the land rises into bluffs, two hundred feet high, composed of a hard yellow earth, alternating with sedimentary rocks. The station was carefully examined for local attraction, by taking fore and dues sights with a compass, but none could be detected. Panama, New Granada. The ship was swung in this roadstead, on May 20th, 1866, in the usual manner. Her position at the time was lat. 8° 55’ N., long. 79° 30’ W. Joint XII on the after turret was 5.5 inches to port. While we were lying here the ship was swinging freely in all directions to the wind and tide. MAGNETIC OBSERVATIONS. et The observations taken on shore, May 14th, were made on the northern side of Flamenco Island, to the westward of a small cocoanut grove, and northeast of the Naval Cemetery. The instruments were set up about ten feet north of the most western of the ruins which are to be found there. ‘The island is rocky, but at this station the rocks are covered with earth. The spot was carefully tested for local attraction by taking fore and back sights with a compass, but none could be detected. If we assume the position of the northeast bastion at Panama to be lat. 8° 56’ 56” N., long. 5 18™ 4°.6 W., as given by Capt. H. Kellet, R.N., then, according to the English Admiralty Chart, the position occupied by the instruments is in Rage (82 od SUN, ong. 5%) 18?) 14.8 W. Acaputco,. Mexico. ‘The ship was swung in this harbor, on June Ist, 1866, in the usual manner. Her position at the time was lat. 16° 50’ N., long. 99° 52’ W. Joint XII on the after turret was 5.5 inches to port. During the three days we were lying at Acapulco the ship was swinging freely to the wind and tide. At the extreme south end of St. Lucia Bay, in this harbor, are two cocoanut groves, tle most western of the two containing the graves of a number of our naval officers. ‘The western end of the eastern grove is the place where the observations taken on shore, on May 30th, were made. ‘The trees come almost close down to high-water mark, and the soil is a gray sand. The instruments were set up about forty feet from high-water mark, at a spot from which the true bearing of the gate of Fort St. Diego is N. 6° 22’ E. If we assume the position of this gate to be lat. 16° 50’ 56” N., long. 6" 39™ 29°.0 W., as given on the English Admiralty Chart, then, according to that chart, the position occupied by the instruments is in Ihate, SiG a0) ) 37 N. Long. 6° 39™ 29°.4 W. MAGDALENA Bay, Lower California. An attempt was made to swing the ship in this bay, on June 9th, 1866, in the usual manner, but owing to a very stiff breeze which was blowing at the time, she could only be tumed through fourteen points. Her position was lat. 24° 38’ N., long. 112° 6’ W. Joint XII on the after turret was 5.5 inches to port. During the three days that we lay in this bay the wind was so strong that the ship did not swing to the tide, but rode with her head con- stantly to the west. As it is difficult to describe the land-marks here, the most convenient way of giving positions will be to refer them to the English Admiralty Chart, the position formerly occupied by Capt. Sir Edw. Belcher’s observatory being taken to be lat. 24° 38’ 18” N., long. 7° 28™ 25%.4 W., as given on the chart. On June 8th a landing was effected at a spot on the beach, about a mile south of the position of Capt. Belcher’s observatory, for the purpose of making a set of magnetic observations; but, after getting a time sight, it was found that there was a great deal of local attraction, nearly all the stones on the beach being magnetic, and consequently it was useless to attempt anything there. ‘The approximate position of this spot is 12 REPORT ON Tat. 24° 38 N. Long. 7 28™ 24° W. On June 9th, after going to the extreme northern end of the bay, and pulling a short distance up a creek, a place was found which, upon careful examination by taking fore and back sights with a compass, seemed to be entirely free from all local attraction. ‘The land there is composed of fine white-sand hillocks, which are constantly being shifted by the wind, and are so loose that aman will sink half way to his knees in walking over them. ‘The only place where the surface was sufficiently solid to admit of the instruments being set up was below high-water mark, where the sand was wet. A complete set of magnetic observations were made there, which, however, were not as satisfactory as could have been wished, owing to~the magnets being disturbed by a stiff breeze which shook the instruments, and from which there was no shelter. ‘The position of this station was Tat. 24° 39’ 36" N. lone, OS YE2 Wy, It was on the east side of the creek (on its left-hand bank), at a place where there is a sharp bend in its course, and can easily be found by plotting the ‘position, given above, on the chart. San Disco Bay, California. We were only in this harbor from 11 A.M. of June 15th, 1866, till 11 A.M. of June 16th, and there was no time to swing the ship. However, during the afternoon of the 15th a complete and very satisfactory set of magnetic observations were made on shore at a spot on the beach near the extreme southern end of the slightly rising ground at La Playa. The instruments were set up just above high-water mark, and nearly due east of the U.S. Coast Survey Astronomical Station. The true bearing of the light-house on Point Loma was 8. 3° 56’ W., and its distance exactly two statute miles in a direct line. The spot was tested for local attraction by taking fore and back sights with a compass, but none could be detected. The position of the station, according to the U.S. Coast Survey Chart, was Lat. 32° 41’ 58’N. Long. 7 48™ 52°.6 W. San Francisco, California. The ship was swung in this harbor, on June 23d, 1866, in the usual manner. Her position at the time was lat. 37° 48’ N., long. 122° 22’ W. Joint XII on the after turret was 5.3 inches to port. While we were lying here the ship was swinging freely to the wind and tide. © The observations taken on shore June 26th were made on the sand beach in a cove on the east side of Yerba Buena Island, the instruments being set up just at high-water mark, and about one hundred and fifty feet north of a long pier which runs out over a mud flat. The place was tested for local attraction by taking fore and back sights with a compass, but none could be detected. | According to the U.S. Coast Survey Chart the position of this station was Lat. 387° 48’ 46’ N. Long, 8" 9™ 225.6 W. MAGNETIC OBSERVATIONS, 13 SECTION III. ASTRONOMICAL OBSERVATIONS. TuE observations contained in this section were all made on the sun, and are for the determination of latitude, local time, and true bearings. ‘The instruments used were a prismatic sextant of six inches radius, by Pistor and Martins; a mercurial artificial horizon; and a pocket mean time chronometer, by Fletcher, marked number 906. The index correction of the sextant was usually obtained by measuring the diameter of the sun, both on and off the arc. For determining the density of the atmosphere thermometers with Fahrenheit scales, and a mercurial barometer graduated to English inches, were employed. The refractions have been computed by means of BessE’s tables, as given in Loomis’ “ Practical Astronomy ;” from which book the tabular parts of the reduc- tions to the meridian have also been taken. The necessary fundamental data have been obtained from the American Nautical Almanac. Observations of circummeridian altitudes of the sun for latitude were made in sets of twelve, so arranged as to eliminate both the sun’s semi-diameter, and all errors depending on the roof of the artificial horizon. Circummeridian Altitudes of the Sun for Latitude, observed at the south front of Fort Christian, St. Thomas, November 17th, 1865. LO SEOs ros° 14! 20” Index correction. 55 48 I5 20 2590 wl to. OF Nersen sor 56 14 16 50 20 TI IO 16 10 . Toy ie risk | 2) II 40 16 20 II Oo 31 21 40 SS | ix 5 22 20 35 II 20.0 Onn 00)1) 26.7 Tiss 104 18 t0 eG) 18 20 Correction =+16' 16”.7 6 I 2 i 28 - a 20 Exe therycge 3 59 TOs 5 fallin WAS SD 4 29 18 40 Bar. 30.16 inches. Mean of chronometer times : : : ; mene Om = 2870 Chronometer slow of local mean time A s t anor fol 47.2 Equation of time é : : : 3 : S + 14 47.1 Local apparent time . : : : - = LU Sse 30:4 Mean of observed double slides - ? F 3 AOA’ ASL 10) «2 Index correction . : : 5 : 5 + 16 16.7 Apparent altitude of sun’s are 5 - 2 : oe S2) p32" 616.0 Refraction . A ; E . : : ‘ 4 — Or 42.1 14 REPORT ON Parallax . ; ‘ : te Hid : 4 oe OP Bho Reduction to mei dle : : é : : : + I 19.4 Sun’s declination : é : : ‘ : : ——I9 6 50.1 Latitude . ; s . uy : : i 5 5 ne we GM IN, Circummeridian Altitudes of the Sun for Latitude, observed at Isle Royal, Salute Islands, November 28th, 1865. nO Te oP, nag? ey ge! Index correction. Tessas 49 ~30 359° 11’ 10” 0° 16’ o” I5 9.5 49 30 6) Ir 10 i} © is A 49 20 a SS SS 16 24.5 48 50 359 II 10 © 16 o Wy Tha 48 40 17 38 126 52 Io ] Correction =+16' 25”.0 18 14.5 51 10 20 17 48 20 = Ex. ther. 91° 2I 9 46 10 2) At. ther. 85 31 46.5 Ge © Bar. 30.13 Inches. e2gO 26 50 Mean of chronometer times 5 : Ba) ib « > TO? IGF BIO Chronometer slow of local mean ee 2 : : 5 ik 26 TOA Equation of time 3 : : : : A : st ALG Local apparent time . : ; : : j 6 TQ Lk 36:0) Mean of observed double nlRinales : ‘ : : . 126° 15’ 55’.0 Index correction 5 0 . é : + 16 25.0 Apparent altitude of sun’s ‘Centre : ° 3 é . 63 16 0.0 Refraction . : broke : 0 5 : — Oo 27.1 Parallax . ; : 6 : c : ; a+ Oy a6) Reduction to saariava + 2a Sun’s declination : ; . 3 : : : SP BA OK Latitude . : : ; : : : : SS eet eZ OMENE Observations for time were usually made in such a manner as to eliminate both the sun’s semi-diameter and all errors which might be produced by the roof of the artificial horizon. For full details of the method see page 33 of the “ Reports on Observations of the Total Eclipse of the Sun, August 7, 1869,” published by the U.S. Naval Observatory, Washington. ~ The reduction of the observations for time has been effected by means of the following formule: — EO ge One® ‘ ee 2 sin 3¢ = sin (SS — a) cos Ssec @ cosec d di=t +¢7— 7 T = mean of observed chronometer times. _A =mean of observed double altitudes. @ = index correction, 7 = refraction. p = parallax, MAGNETIC OBSERVATIONS. a = true geocentric altitude of sun’s centre. d =sun’s polar distance, measured from the elevated pole. = latitude of place where observation is made. ¢ = hour angle at the pole. tv = equation of time. 15 dt = correction of chronometer to reduce the reading of its face to local mean time. October 29th, 1865. gh ue he 49° 27! 50” sit el: 38 20 Rize 22 49 30 20 Index correction, oo23 5) i .A° 53 56.5 17 50 = +15) 42” 54 47 SOS 2 320 B5ieo° 49 47 0 56 25 57 20 56 57:5 50 6 20 Lion , 57 59:5 24 50 = 58 32-5 34 30 59 13:5 45) 5° Ex. ther. 50°. At. ther. 92°. Bar. 30.40 inches. Refraction = — 125” 7 Sun’s declination — 13° 35’ 16” Paral axeee——7-1=) nS Latitude +36 49 32 Mean of observed double altitudes. : : 4 a 50> 39, 24" Local apparent time . : : : ; : . wot 8 Om 4088 Equation of time “ : : < 2 : : —_ 16 10.6 Local mean time : 5 : : : : ; = 1S) SOmgor2 Mean of chronometer times : 6 é ° c Sy GE ge Chronometer fast of local mean time . 3 4 . fa Ok ede Abed Longitude west . . ; : : : [ue Shona yt:, Chronometer slow of Greenwich mean time - : SONGS es sey October 29th, 1865. iri? slate ZOURTO TO, 12 54 201m 5 20 :3s 255 38 30 22) Index correction, 4A ngs 40 30 30 a uit pat ye) =-+15 42 15 36.5 220 A= 16 52.5 39 37 30 o LG ay 23. 10 18 24.5 8 30 19 16.5 37.040) 10ties: 3I 30 i 2© 20) 55.5 20 10 ) Ex. ther. 55° At. ther. 79 Bar. 30.36 inches. Refraction =—170".1 Sun’s declination — 13° 40’ 42".0 Parallax =+ 8.0 Latitude +36 49 32. Mean of observed double altitudes. F r ‘ am zo° (16% 23!03 Local apparent time . : , ; 5 . : egy 27 ™ ET Double Altitudes of the Sun, for Time, observed at the flagstaff in the Navy-yard at Portsmouth, Va., Double Altitudes of the Sun for Time, observed at the flagstaff in the Navy-yard at Portsmouth, Va., 16 REPORT ON Equation of time . 0 6 P 5 . ; .— of 16™ 115.6 Local mean time : : : : 6 : : 5 Bo HT ACLs Mean of chronometer times t 5 é . : 5 8 TO FOAL Chronometer fast of local mean time . : : . 0 © A AeE Longitude west . 5 5COQ.8 Chronometer slow of Cuesnnrialn mean 1 he 5 © BO" Double Altitudes of the Sun for Time, observed at Fort Christian, St. Thomas, West Indies, November 13th, 1865. 9g? om 425.5 84° 32’ 50” it Biro 46 20 Index correction. 2 fe} : 2.5 85 2 oS 20 359° Io’ 50” 0° 16’ 207 ay dh 35 10 ii © 16 10 4 54 85 51 Oo II Io 16 4o 6 0.5 87 15 20 6 41 28 30 359 II 0.0 © 16 29.87 10 37 6 | 20 , ee Wy BALI 50 20 Correction =+16' 187.4 8 21.5 59 20 | 8 48.5 88-7 Oo Ex. ther. 84° At. ther. 86° Bar. 30.12 inches. Refraction =—57".7 Sun’s declination —18° 5’ 2/5 Parallax =-+ 6.2 Latitude = OWEZON 276 Mean of observed double altitudes . 0 5 c . 86° 26’ 25/8 Local apparent time . : ; : : 5 : qo eLOn 320550 Equation of time 6 . é : 0 : : = 15 31.2 Local mean time : 9 45 48.8 Mean of chronometer times : QO 8 Fe Chronometer slow of local mean time © 40 43.6 Longitude west . 4 19 42.7 Chronometer slow of Gueenvica mean are R © A63 Double Altitudes of the Sun for Time, observed at Isle Royal, Salute Islands, November 28th, 1865. gh Ag@ 585 109° 53! 20" 48 35 IIo 9 50 Index correction. 49 8 20 Oo 20 49 58 35: 30 (ira gee cooler 0° 15’ 50” 50 31 45 50° II oO 16 0 50 «(56.5 52 50 Io 50 16 Io 5I 44.5 Di 13 © -——— 52 39-5 30 © 359 I0 56.7 °o 16 0.0 53 13-5 diy) 260 . Ake 53 «47 5 © Correction =+16' 317.6 54 19 173 © © 54 53-5 i © | Ex. ther. 93° At. ther. 85° Bar. 30.13 inches. Refraction = — 36.3 Sun’s declination — 21° 23’ 307.3 Parallax =+ 4.9 Latitude + 85 17 29. Mean of observed double altitudes . 5 c : . 111° 35’ 267.6 Local apparent time . : ‘ : ; : : Re Lonese Sr aEnS, Equation of time , 3 : ‘ : : ‘ — Il 43.8 Local mean time : : : 5 : é . I0 2r 48.0 Mean of chronometer times : a 5 a : - 8 51 28.6 MAGNETIC OBSERVATIONS. abs 7 Chronometer slow of local mean time. : é - a) Laesos not4 Longitude west . : : c : : : eg SOutT. 4 Chronometer slow of Greenwich mean time : : ia Pulp pele fobrs Double Altitudes of the Sun for Time, observed at Ceara, Brazil, December 13th, 1865. Ut ~>pets acter G22 Index correction. 15 58.5 62 40 o 16 41 20 0 20 Z5OmexL SO Oo 160, rip eR LO) s.0 Io 50 10 17 26 G20) 76 Io 40 ° 18 43 62 30 o — TOM es ZOO 359 I0 50.0 On TO) 1323 19 26.5 Io oO 20 19 50 62.0) Jo Correction =+16' 33.3 20m) Wis 6r 50 70 Ex. ther. 84° At. ther. 82° Bar. 30.05 inches. Refraction =— 89".5 Sun’s declination — 23° 12’ 4”.0 Parallax =+ 7.4 Mean of observed double altitudes. = < : 702°. BG Ov-0 Mean of chronometer times : : : : ; ipa aes Equation of time : F . : : : , — BP at20:9 Reducing this observation with latitude = — 8° 43’ 15", we find the chronometer 2" 26™ 29°.6 slow of local mean time. Reducing it with latitude = — 3° 44’ 15”, we find the chronometer 2" 26™ 32°.0 slow of local mean time. Double Altitudes of the Sun for Time, observed at Ceara, Brazil, December 14th, 1865. ~>ae 2 On.5 99° 30° «6 Index correction. 2 24.5 40 0 2 49 FOmO 20 350" EO) 30% 0° 16’ 10” Ze bass LOOM Ono 40 20 - 3 36 EO. 6 4o 20 67 9 ECO) LO" =1C Gr s2t5 20m 10 259) £O) 30.7 On 1O™ LOr7 Gras 30 #20 2 ‘ G Ptals 46, 0 Correction =+16' 33”.3 7 ARs 100 50 0 Ex. ther. 81° At. ther. 82° Bar. 30.12 inches. Refraction =— 45".9 Sun’s declination — 23° 14’ 46'’.2 Parallax =-+ 5.6 Mean of observed double altitudes. 2 : : Fitelols Silo = fol ao) Mean of chronometer times A é 7 c ‘ 5) GF BES Equation of time : 5 ; : : : : — 4 59-5 Reducing this observation with latitude = — 3° 43’ 15”, we find the chronometer 2 26™ 33°.7 slow of local mean time. Reducing it with latitude = — 3° 44 15’, we find the chronometer 2° 26™ 30°.9 slow of local mean time. 3 February, 1872. 18 REPORT ON Double Altitudes of the Sun for Time, observed at Ceara, Brazil, December 14th, 1865. res es 100° 50’ oO” | Index correction. 52 14.5 40 052 By 30 0 | 20 359° 10’ 50” OO Tis! Bey Re ok 20 o | 40 16 20 53 206 Io o | 20 16 oOo 56 0 Sino Pon ———— 56 23 97 509 0 359) 10, 830-7 O16) 323 56 48 4o oO 2© : Sy io 30 +O Correction =+16' 40”.0 Si St 20 0 Ex. ther. 86° At. ther. 83° Bar. 30.00 inches. Refraction = — 45”.6 Sun’s declination — 23° 15’ 277.4 Parallax =+ 5.6 Mean of observed double altitudes . : : : 5 OP 5 oC Mean of chronometer times 5 . c : : 5 nS A 1G Equation of time : é . : : : 3 — A Be e4] Reducing this observation with latitude = — 8° 43! 15", we find the chronometer 2" 26™ 30°.7 slow of local mean time. Reducing it with latitude = — 38° 44’ 15", we find the chronometer 2" 26" 33°.1 slow of local mean time. In order to determine both the latitude of Ceara and the error of the chronometer from the three observations which have just been given, we proceed as follows: Comparing the error obtained on the afternoon of December 138th, with that obtained on the afternoon of December 14th, we find that the chronometer was losing 1.17 seconds per day; and this rate is independent of any small change in the adopted value of the latitude. By means of this rate, reducing all the observed chronometer errors to 2" 26™ P. M. December 14th, and then plotting them according to Sumner’s method, we get for the place of observation Latitude 3° 43’ 59’ S. and for the chronometer, Chronometer slow of local mean time . : o 5 5 ot 26 95 Longitude west . ‘ Bahay ao : : : c Be a 8 Chronometer slow of Greenwich mean time . 0 : 6 § © ache Double Altitudes of the Sun for Time, observed at Pernambuco, Brazil, December 23d, 1865. Ae aoe ix nig ney Gi" Index correction. 30 39.5 20 oO [0 359° Io’ 50” 0° 16’ oO” BiB 30 Oo 50 16 ro BA BOK 118 I0 o —_ | ——_—_—__—— Bo, 13 ZOM ON a2) 359 10 50.0 © 16 5.033 40 30 oO ‘ Correction =+16' 32.5 Ex. ther. 83° At. ther. Bar. Refraction = — 32”.1 Sun’s declination — 23° 26’ 31” Parallax =+ 4.5 Latitude — 8 3 37 Mean of observed double altitudes . ¢ : 5 5 ne? ae Le Local apparent time . ¢ : 6 : j 3 2 1h G2 265 Equation of time : . : : ; : : — OQ gr.# Local mean time : 2 0 : e : . 6 HO 8 92.35 MAGNETIC OBSERVATIONS. _ Mean of chronometer times : Chronometer slow of local mean time Longitude west . Chronometer slow of Gresnwieh mean time Double Altitudes of the Sun for Time, observed at Bahia, Brazil, December 27th, 1865. 6® 52™ ros 98° 30' : Index correction. Cee hig. ACPO) 7-26) @ 3595 10! Mor cole) file fel Ban 54.5 5° Oo 50 ° 54 32 98 30 0 ah 54 5355 40 Oo }:0 359 10 45.0 o 16 -O 55 16.5 Rey, Correction =+16! 35".0 Ex. ther. 88° At. ther. Bar. Refraction =— 45’.9 Sun’s declination — 23° 19' 33.8 Parallax =+ 5.7 Latitude —I2 56 55. Mean of observed double altitudes 98° 40’ 0.0 Local apparent time . a GS ve ete Equation of time + Ti 27-3 Local mean time : 9 15 49.8 Mean of chronometer times é 6 53 43.0 Chronometer slow of local mean time 2422 0-8 Longitude west . : 224) 50-5 Chronometer slow of Grecavich mean time 456 733 19 Double Altitudes of the Sun for Time, observed at the Light-house in Fort St. Antonio, Bahia, Brazil, December 29th, 1865. Fa © ae a migysi yey fa! Index correction. LSet me a Nee xe) iy gu TO) 0 2Q 359° 10’ so” O76" 20! 15 56 20) 16 5° Io TO Lous 20, 0 40 ste) Ly) L7G 134 50 Oo 17 44 ese Ou eo 359 10 46.7 O16 657 rS'9 7) oy fs, 20 18 31.5 0) | Correction =+416’ 33.3 18 54 Be) a) Ex. ther. 84° At. ther. Bar. Refraction = — 22”.1 Sun’s declination — 23° 13’ 31'.1 Parallax =+ 3.3 Latitude =i) se Mean of observed double altitudes 1 LS ay aol: Local apparent time . : : 5 5 : “ To? 36™ 25°.47 Equation of time : : : : - : + 2 27.6 Local mean time ; : : - 5 : Io 38 53.3 Mean of chronometer times : 8 16 49.7 Chronometer slow of local mean time 2.22 3.6 Longitude west . : . aga 6.0 Chronometer slow of eeenwicn mean time 4 56 10.5 20 REPORT ON Double Altitudes of the Sun for Time, observed at Rio Janeiro, Brazil, January oth, 1866. Be Tg wip 47° 40’ oo” Index correction. 13 39 5° 6 ORS 359° 10’ 40” OP if ol HAL Bok. AS © © 30 I5 50 14 26.5 Io (oO SS aa 15 43 47 40 0 85 HO HH) Q 15” Base) 166 «68 5 © SO F ie 16 29 48 0 0 = Correction =+16' 45'.0 16 53 Io 0 | Ex. ther. 74° At. ther. 77° Bar. 29.94 inches. Refraction = — 123”.2. Sun’s declination —22° 6’ 24’.6 Parallax =+ 7.9 Latitude —22 84 8. Mean of observed double altitudes. : : , 5 AP 33’ O'S Local apparent time . a ; : ‘ : 6 9 iO RSG Equation of time . ° ; : : : : + 4 23.8 Local mean time 5 7 18 43.3 Mean of chronometer times : B i AG Chronometer slow of local mean time B 2 Bou Longitude west . , 2 RD On| Chronometer slow'of Gaaenvfech mean time A, 56) Bait Double Altitudes of the Sun for Time, observed at Rat Island, harbor of Rio Janeiro, January oth, 1866. {7 Index correction.Pe On 1S? G Go }| 27 20 1 © | 27 42.5 2 © AG) s8G° me’ 30" ring gel 28. 4.5 3 © || : 4o 50 28 26.5 40 Oo { 40 50 29 21 TOS OO 29 45 Io o | 359. 10 36.7 © 15 50.0 39 20) 10) 2© 30 26.5 30 Oo | Correction =+16' 46”.6 30 48 40 oO Ex. ther. 75° At. ther. 77° Bar. 29.94 inches. Refraction = — 39”.8 Sun’s declination —22° 5/ 377.3 Parallax =-+ 5.1 Latitude 22 8A AG Mean of observed double altitudes. : ; : . 108° 20’ 0.0 Local apparent time . : s : : : : 5. OF AST C7 Equation of time ‘ A : ; : F ‘ . + 7 26.0 Local mean time F 9 32 26.7 Mean of chronometer times : 7 28 53-9 Chronometer slow of local mean time QB Bente Longitude west . ¢ 5 2) 52 3769 Chronometer slow of Ghose mean time 4 56 10.7 Double Altitudes of the Sun for Time, observed at Monte Video, Uruguay, January 18th, 1866. 45 o™ 265.5 ADS OmOn Index correction. : co) af 40 Oo 20 359° 10’ 30” Co ig! Be" I I 30 ° = 40 4° A Bol Io 6(O 40 40 3) eo 45, 59 © rae mi : oe 4o Oo | 26 359 10 36.7 © 15 43.3 : 30 Oo 4 46 i © | Correction =+16' 50”.0 MAGNETIC OBSERVATIONS. 21 Ex. ther. 76° AtS ther.» 79° Bar. 30.02 inches. Refraction =— 130".2 Sun’s declination — 20° 26’ 55.2 Parallax =+ 8.0 Latitude —34 53 39 Mean of observed double altitudes. ; : : = 480) 32 2301.0 Local apparent time . ; : : : : ; 5 GE ee See: Equation of time : ‘ , : : : + Io 51.4 Local mean time : BES 5050 Mean of chronometer times ° Am 2 2066 Chronometer slow of local mean time © i 27.0 Longitude west . ; : : : : 3 44 55.8 Chronometer slow of Greenwich mean time 4 56 22.8 Double Altitudes of the Sun for Time, observed on Rat Island, harbor of Monte Video, Uruguay, January 24th, 1866. DASE Gis EI eye eh Index correction.. 29 «25.5 20 0 29 «50.5 ne} 20) 359. bo" io! OPMESi AO” Bor ss SZ Ohm Io 10 40 30 38.5 Ste50) 0 Io 10 20 ZI 38.5 82.30) 0 | eecpm e 20 0 359 10 10.0 Owetsen 3353 32 26 ule} fo) 26) B20 eat SZ OmeyO aml Correction =+ 17’ 87.3 32716 Sreson ons) Ex. ther. 74° At. ther. Bar. Refraction =— 62”.7 Sun’s declination —19° 6’ 337.8 Parallax =+ 6.5 Latitude — 34 53 18 Mean of observed double altitudes. c : “ oF ECZE RTO GNO..6 Local apparent time . : : i é : : Se BE Be By, Equation of time E : : ; : : : + 12 29.2 Local mean time F 3) 142 = 3419 Mean of chronometer times : PHEW ube ey.| Chronometer slow of local mean time Dies 2055 Longitude west . : : : é : 3 44 52.9 Chronometer slow of Greenwich mean time 4 56 19.4 Double Altitudes of the Sun, for Time, observed at Sandy Point, in the Straits of Magellan, February 7th, 1866. =i Index correction.9" 59™ 24°.5 go° 30’ 0 Io o II 4o 0 ee 50. 0 20 850% lO zon Oy euhee40y I 49.5 jlo Oo 30 50 2 37-5 io) 6 35 35 4 39-5 go 30 0 === Gy ial 40 oO BuOmitOu 20.3 ©. 15 41.7 S18:5 EO 10 20 : 7 9 Oy Tey | Correction = + 16’ 55”.0 7 58.5 Io Oo Ex. ther. 52° At. ther. 70° Bar. 30.04 inches. Refraction = — 56.9 Sun’s declination — 15° 14’ 15”.6 Parallax =-+ 6.1 Latitude —53 I0 20 Mean of observed double altitudes. : : : - go° 50’ 0” Local apparent time . ‘ : 2 : : : 2.) IoD eae Equation of time : ; : - : : : + 14 25-5 REPORT ON Local mean time ‘ P F 3 : : : 5 ne OS BPG Mean of chronometer times : : : 6 : LOMO FO Chronometer slow of local mean time © 12 48.1 Longitude west . AL AQ Bie Chronometer slow of Gasonncln mean time 4 56 23.4 Double Altitudes of the Sun for Time, observed near Valparaiso, Chile, March 2d, 1866. gt go ELS 62° CHOY Index correction. 5° 39-5 Ox 5 © 20 359° 10 4o” OF un ol SES 7 © = 45 5 5I 51.5 RO) © 4o 10 BR §e 62 S © ——— SS 53 15-5 Se 9 OW ee SBN HO” ed Qypaegy GeO 5g heb 49 @ , 54 30 20 0 Correction =+ 17’ 67.6 Ex. ther. 67° At. ther. Bar. Refraction =—92”.4 Sun’s declination — 7° 1 53” Parallax =+ 7.4 Latitude = 33, Tod Mean of observed double altitudes. : 5 4 . 61° 42’ 30.0 Local apparent time . é i é : ; 6 0 SF AGE ME.9 Equation of time : : : ; F : : a+ TA TG) Local mean time ‘ AB BB Mean of chronometer times 0 9 fe TES Chronometer slow of local mean time © 9 46.4 Longitude west . 4 46 31 Chronometer slow of Gaaonriah mean acme 4 56 17.4 Double Altitudes of the Sun for Time, observed in Valparaiso, Chile, March 29th, 1866. BP 20" 85° eS OO u Index correction. By AG 05 e ie 359 20” 0° 14 50” 38 23 Qo © 50 45 40 1.5 13, G2 © ‘ 45 5540 45-5 ie Sl Ss a 41 28.5 °o oO )26 359 10 38.3 © 14 50.0 Correction = + t7’ 15”.8 Ex. ther. 71° At. ther. 69° Bar. 30. 23 inches. Refraction = — 75”.1 Sun’s declination + 3° 31’ 38” Parallax =-+ 6.9 Latitude —33 1 47 Mean of observed double altitudes . : : : 5 GS? x’ © Local apparent time . : : : 5 : 2 a) OS AGE Reh.© Equation of time : i 5 : 5 5 ‘ + 4 47.0 Local mean time 3 2 48 39.0 Mean of chronometer times : QA OG) 12,2 Chronometer slow of local mean time. ° 9 26.8 Longitude west . 4 46 45.7 Chronometer slow of Grasamioh mean time 4 56 12.5 Double Altitudes of the Sun for Time, observed in Valparaiso, Chile, April yth, 1866. g® 36™ 26%.5 ine 33 Index correction. BH ROS AS @ PAG) AEG? uc! Bo” Ons ero 38 «6 78 Qo © 50 Be) A) ii i go © 50 10 40 53 45 0 }2Q —————_|—___ 41 44.5 78 ne) 359 IO 50.0 © I5 10.0 Correction = + 17’ 0”.0 a MAGNETIC OBSERVATIONS. Ex. ther. 67° At. ther. 65° Bar. 30.17 inches. Refraction = — 69".8 Sun’s declination + 6° 53’ 28.6 Parallax =-+ 6.7 Latitude —33 I 47 Mean of observed double altitudes. : F é 2) 77° VAR. volo Local apparent time . ‘ : : - : : 7) 98) 46™ 1056 Equation of time : : P « t - : + 2 8.9 Local mean time : 9 48 28.5 Mean of chronometer times : OF sow, int Chronometer slow of local mean time OM G2 23 Longitude west . 4 46 45.7 Chronometer slow of pent mean cae 450) 9-6 Double Altitudes of the Sun for Time, observed in Valparaiso, Chile, April 7th, 1866. 9" 43™ 15%5 edb g Be oa oe i A4, 6.5 45 © 726 Index correction 45 0.5 80 0 o ) 46 57 79 30 0 i) =P a7, 0.0 47 49-5 45 © +20 48 44.5 Som 07 0 j Ex. ther. 67° Atther 652 Bar. 30.17 inches. Refraction =— 67".3 Sun’s declination — 6° 53’ 35.4 Parallax =+ 6.6 Latitude a oA) Mean of observed double altitudes. : 7 . = 792 Aa) OG Local apparent time . a . : : ; Ona ™ Er Asi Equation of time : : * : : ; : + Gi tats Local mean time 9 55 22.8 Mean of chronometer Aes 3 Oue4d5 58:0 Chronometer slow of local mean time © G 2eho) Longitude west : : 4 46 45.7 Chronometer slow of Grecawich mean time 4 56 9.6 Double Altitudes of the Sun for Time, observed in Valparaiso, Chile, April 14th, 1866. Eso" 20% Goesom nor Index correction. : 2 ae g _ ° es 359° 10° 40” Ol eid eE oO! 5I 39 ° ° 40 45 SSaal 36 30 0 = 45 50 53 46 HB) MD) (AO) ae a 54 24.5 Qo ~o 359 10 41.6 OF 0470.48.32 Correction = + 17’ 15".0 Ex: ther. 65° At. ther. 66° Bar. 30.13 inches. Refraction =—170",3 Sun’s declination + 9° 33’ 33”.6 Parallax =+4+ 81 Latitude SR a ey Mean of observed double altitudes. : - : Mes Oun Tn eROneG Local apparent time . : - : : : : Sey Cite ecti ity Equation of time. : - : : : : ~+ o 11.6 Local mean time 4 Mean of chronometer nee : ; 3 Chronometer slow of local mean time : 5 : che! Kel pauiige Wie: Longitude west . : 4 Chronometer slow of Greenwich mean time 4 24. REPORT ON Double Altitudes of the Sun for Time, observed on the Island of San Lorenzo, near Callao, Peru, April 26th, 1866. Index correction.As 123° 0 oo” 18 52 I5 0 j-0 359° 11’ 10” - SO ay oi FI) + 30 +O 10 ) 22 46 1A © © SS SSS === = 24 «2 I5 oO 9 359 II 10.0 © 15 | Oe 25 18 390 Correction = +16’ 55/0 Ex. ther. 80° At. ther. Bar. ry Refraction = — 29.2. Sun’s declination -+ 13° 35’ 187 Parallax =-+ 4.0 Latitude —I2 5 14 Mean of observed double altitudes . , : 5 5 mA? TR CM A6) Local apparent time . j : : c F ‘ 6 HEE TA SOB Equation of time : : : : : : - — 2 18.8 Local. mean time a ; 5 c j A s 5 i 1) el Mean of chronometer times : E : 9 ; 5 i Bi ayy Chronometer fast of local mean time . : : 6 =) PO a ergas Longitude west . : : . Sh SS AGN Opus Chronometer slow of Gacouvich mean ‘ane : . 5 A By E20 Double Altitudes of the Sun for Time, observed at Payta, Peru, May jth, 1866. 88 4o™ 44°.5 62 Gf oo Index correction. Ai Thfol3 ig © Lo 359° II 30” O° ny’ ol! AI 51 30 Oo 25 fo) AQ Thal 62 0 oO 25 ° 43 34-5 15 0 [9 ay Aa es 30 +O BG) nit ADs) © I5 0.0 Correction = + 16’ 467.6 Ex. ther. 78° At. ther. 80° Bar. 30.06 inches. Refraction = —090".7 Sun’s declination -+ 16° 50’ 46” Parallax Sdb FR Latitude =f 8 26 Mean of observed double altitudes . : ¢ . 5 O15’ OS Local apparent time 8 ro™ 225.3 Equation of time é ; : : : : a — 3 38.1 Local mean time : 8 15 44.2 Mean of chronometer times j 8 42 26.1 Chronometer fast of local mean time . o 26 41.9 Longitude west . : 5 24 22.0 Chronometer slow of Crean mean time A ee AOnt Double Altitudes of the Sun for Time, observed on Flamenco Island, Panama Bay, May 14th, 1866. 9h 24™ 505 O° of oO! Index correction. as Bu uy © lo asg? nn’ so" Oo 15’ ne” 26 863.5 30 ~O 20 I4 55 27 12 O93, © © 20 14 40 27 43-5 Too Lo ——|———_—__—_ 28 15 32 © 359 IL 23.3 © i4 55.0 Correction = + 16’ 50’.8 Ex. ther. 385° At. tner. 85° Bar. 30.10 inches. Refraction =— 49".5 Sun’s declination -+ 18° 39’ 49” Parallax =4- 5.7 Latitude + 8 54 31 oe ~ MAGNETIC OBSERVATIONS. Mean of observed double altitudes. : : ‘ SLOn: SLSiaay-O Local apparent time . ; - ; ; : : SOR tOsenss cn Equation of time : : : “ » : — Sues ank Local mean time 9 Mean of chronometer times : = 9) 268 53752 Chronometer fast of local mean time . : : : =O) 20M snOsg Longitude west . be lop shee Chronometer slow of Grocawich mean time 4 57 44.9 Double Altitudes of the Sun for Time, observed at Acapulco, Mexico, May 30th, 1866. To™ 25™ 36° Soe oumn OF Index correction. 26000 5.5 sie) ha 359° x11’ to” Ch Sins eit 26 38.5 30 «20 ° 14 40 27 49.5 30m OmenO 20 The 16 28 22 ni) {0 ——$ _—_—— —_——_ 28 54 B20) 0 Shou sit | LO:0 OM TAS ahs Correction = + 16’ 58”.3 Ex. ther. 89° At. ther. 85° Bar. 30.10 inches. Refraction = —54".5 Sun’s declination + 21° 48’ 7” Parallax =+ 6.0 Latitude +16 50 3 Mean of observed double altitudes. : : é 2 89ers, OO Local apparent time . 3 : : : : ; eS 4st 36.4 Equation of time “ F ; : = : ; — 2 46.4 Local mean time c : : A - : = OAs 5220) Mean of chronometer times : : : , LOM 2 TAye2 Chronometer fast of local mean time . . : A ok Anil 222 Longitude west . 3 c - ~ 6239) 29:4 Chronometer slow of Greenwich mean time : : Sel ipl eee Double Altitudes of the Sun for Time, observed in Magdalena Bay, Lower California, June 8th, 1866. 52 20™ 408 TOO? 45.0 Index correction. 2r 23 30 0 2©) 359° 10’ 50” Ouetd dow 20 5G Tig) ) TL) 20 I4 50 2a kS.5 TOO" 45, 0 ao Io 30 TsO 2a ATS 30 0 ¢2Q)3__ | 24 «5 ny fe) 200. sLONuSaa4 © 14 50.0 Correction = + 17’ 8.4 Ex. ther. 69° At. ther. 70° Bar. 30.02 inches. Refraction =— 46’.4 Sun’s declination + 22° 53’ 42” Parallax =+ 5.4 Latitude +24 38 Mean of observed double altitudes. F ; < . 100° 30’ 0.0 Local apparent time . : ‘ : ; : : 5 peril Equation of time : : 3 : : : : a te Ack Local mean time 0 Be 52278 Mean of chronometer times : G Be ores Chronometer fast of local mean time . 2308 4-4: Longitude west . : 7 28 24.0 Chronometer slow of Grcavich mean peas = 7 4 58 19.6 4 February, 1872. 26 REPORT ON Double Altitudes of the Sun for Time, observed at La Playa, San Diego Bay, California, June 15th, 1866. 5 16™ 41. 112° 30’ ")) Index correction. 17 16 15 0 +}2© 359° 11’ 30” OP nl’ gol 7 55-5 CeO ) 35 39 Ig 10 ni 3) © ) 20 .50 19 46 1 =O -2O) SE 20 21.5 eC ©) J 359 It 28.3 © 14 43-3 Correction = + 16' 54.2 Ex. ther. 71° At. ther. 72° Bar. 30.12 inches. Refraction = — 37".4 Sun’s declination -+ 23° 20’ 22” Parallax =+ 4.7 Latitude +32 41 58 Mean of observed double altitudes. : : ; 5 Ke? me’ G".O Local apparent time . : : j 5 ; : A ee BS 53 Equation of time 2 z é : : i a+ Q 11.3 Local mean time : 2 Be iB. Mean of chronometer times 2 5 18 31.1 Chronometer fast of local mean time . 2 FO!) Qa Longitude west . : : 7 48 52.6 Chronometer slow of Gresanioh mean time Mk 133} AO)n1 Double Altitudes of the Sun for Time, observed on Verba Buena Island, San Francisco Bay, California, June 26th, 1866. 4" 16™ 408.5 Ws? ig’ SY Index correction. 17 18 | 40 @ ‘ 26) B5O° nn’ 36)" OoTAaeol 17 55-5 45 0 35 5° Ig 18.5 i tO) 25 50 19 54-5 | 39 © ‘ 20 —_—_—_—_— ——_—— 20, 30 45 @ 359 FE gO: So 14 43-3 Correction = + 16’ 53”.4 Bixe thers 675 At. ther. Bar. Refraction = — 72”.5 Sun’s declination -+ 23° 22” 4” Parallax =+ 6.6 Latitude +37 48 46 Mean of observed double altitudes. 6 3 f 2 SO ae C0 Local apparent time . : ‘ : : 3 : 5 SE Rem ieee Equation of time ‘ : : ¢ 4 : : _ 2 29.6 Local mean time 8 S- 5 286 Mean of chronometer times 4 18 36.2 Chronometer fast of local mean time . Sats) he Longitude west . : : 8 9g 22.6 Chronometer fast of Gissmatan mean time. : 2 56 MO 8 ARO The chronometer used in making this observation was T. S. and J. D. Negus’ No. 1287. True bearings were determined by measuring with a sextant the angle between the sun’s limb and some well-defined terrestrial object, the time being noted at the instant the angle was observed. If the terrestrial object was much elevated above the horizon its angular altitude was also measured. Knowing the latitude of the place of observation, the local time, and the sun’s declination, the sun’s zenith distance and true bearing were calculated. Then, having the zenith dis- tance of the sun, the zenith distance of the terrestrial object, and the measured gngle between the sun and the terrestrial object, the horizontal angle between them MAGNETIC OBSERVATIONS. oF was computed, and applying it to the sun’s true bearing the true bearing of the terrestrial object at once became known. The formule employed were as follows. Let T = mean of observed chronometer times. dt = correction of chronometer to reduce the reading of its face to local mean time. a ap of time. é =sun’s hour angle, or the apparent time. Q = mean of ceed angular distances between the sun’s limb and the ter- restrial object. @ = index correction of sextant. s = sun’s semi-diameter. a@ = apparent zenith distance of sun’s centre. b =zenith distance of terrestrial object. ¢ = true angular distance between the sun’s centre and the terrestrial object. C= cheval angle included between the sun’s centre and the terrestrial object. = latitude of the place of observation. A = azimuth, or true bearing, of sun’s centre. ¢ =true zenith distance of sun’s centre. 5 =sun’s declination. y =refraction due to apparent altitude of sun’s limb. B = true bearing of terrestrial object. Then we have i= T+ dt-+¢ | uo = 28 Pee: tan t cos M sin (@ — M) oe tan (» — M1) i he, eos A. where A is to be taken greater or less than 180°, according as ¢ is greater or less than 180°. a= O-—r c=Q+o0+8 If } is exactly 90°, we have cos c sin a cos C=-— But if 6 is either greater or less than 90°, we have pe pa ere ig ED tm $0= 4] sin S sin (S — e) Finally B=Aane 28 REPORT ON In a few instances true bearings were obtained by observing the sun when its apparent elevation above the horizon was equal to its diameter. In that case ¢ = 90° and then caw sin 6 cos @ in which the azimuth will be north or south of the prime vertical according as the sun’s declination is north or south. Observations of the Sun, made October 31st, 1865, to determine the true bearing of the object used as an azimuth mark in swinging the ship at Hampton Roads, Va. to" 10™ 508 127° 20! ni Zi 38 12 15 45 14 0 128 4 14 39 8 Tf Io I2 42 Q TAG AG) Chronometer fast © 4 50 ® + 16 2 + 16 16 g + 16 Apparent time Io 24 8 c 128 19 t 23° 58 g 55 59 5 —14 16 r a ea ¢ 36 58 a 55 58 M S15 3e 6 nearly go e— MU 52 31 C 138 26 True bearing of sun . : 3 ; : ; 5 Sb BS Bi 1h. Z Seminary to sun . é . A 3 ‘ 5 - 138 26 Z Seminary to Rip Raps. , ° * : : 0 62 44 Z Rip Raps to tree. : ; C 5 : 3 0 «RIA BF True bearing of tree . : ; z : 0 . 8S. to 34 W. Observations of the Sun, made November 18th, 1865, to determine the true bearing of the object used as an azimuth mark in swinging the ship at St. Thomas, West Indies. 72 OU S BAe tg! 2 15 15 4 45 10 8 15 12 9 45 12 df? Th) Sus od Q 34 12 Chronometer slow © 40 47 w + 16 7 + 14 36 5 + 16 Apparent time 8 o 24 G 34 44 Z 59° 54) Cee 69 48 6 —iI19 19 r = & © I8 20 a 69 46 M —34 57 4 nearly (fe) e—M 53 17 Cc 28 52 True bearing of sun . 5 ‘ : ; : . S. 60° 27’ E. Z Sun to Peak 5 : : 0 : 5 0 0 28 52 True bearing of Peak . . 3 : 5 é . S. 31 35 E. MAGNETIC OBSERVATIONS. 29 Observations of the Sun, made Novem. er 28th, 1865, to determine the true bearing of the object used as an azimuth mark in swinging the ship at Isle Royal, Salute Islands. 65 27™ Be 74° 50’ 28 59 4 2 8 4o L 6 29 4 Q 74 45 Chronometer slow mye) ai) ry + 17 z + Ir 45 G + 16 Apparent time SRA AS c 75 i8 t BT) wis. g 62 4 5 —— 2 a r = > Ly a O2mee2 MM —35 52 é nearly 90 e—W 4I 9g G 73 «18 True bearing of sun - a : - . . S. 62° 24’ E. ZSunto Nob . F : : : : ¢ : : 72" 0S True bearing of Nob. : : : : ; sao: DON SANW Observations of the Sun, made December 12th, 1865, to determine the true bearing of the object used as an azimuth mark in swinging the ship at Ceara, Brazil. geek 87° 30’ 13 5EO 22 14 32 21 tf Gi 8 Q 87 24 Chronometer slow 2) 920) 32 wo + 16 t cp, yy s Gia 60 Apparent time By dish) tt ¢ 87 56 t 86°. 18! ‘a 8:4 c) eS A = Tie: > aa 13 AS a 84 46 M —8r 25 6 nearly go o— Mm 77° 42 Cc 87 56 True bearing of sun : ‘ ¢ : Os Oyee eQuiW. Z Lantern to sun 3 : : : 5 5 = + 87 56 Z Light-house to Lantern . ; : . . ‘ : ap ke) True bearing of Light-house . F : : : wN. 82: 9 E. Observations of the Sun, made December 29th, 1865, to determine the true bearing of the object used as an azimuth mark in swinging the ship at Bahia, Brazil. When the sun’s true zenith distance was about 90°, the angle between its nearest limb and a con- spicuous tree was measured and found to be 31° 38’, the tree being to the right of the sun. SS ay = 2907 2! True bearing of sun ; : : : : F ses BOW ZSuntotree . < : : : : : 3 Br 233 Sun’s semi-diameter ‘ ‘ . ‘. ; ; ° 16 True bearing of tree. : A a a SON Sad 57 We 30 REPORT ON Observations of the Sun, made January 7th, 1866, to determine the true bearing of the object used as an azimuth mark in swinging the ship at Rio Janetro, Brazil. Bo Bn acl 112° 2 53) 45 7 55 ® 12 T 83. 2G Q Ii2 15 Chronometer slow Bo- B. p o + 17 t = © 3 Ss ad Apparent time 7 SO Bi é Il2 32 t 62° 25/ g 57 @) ) == 228 22 r == I ? — 22 54 @ 57 «8 M — 41 38 b 85 16 e—W@ 18 44 Cc 120 45 True bearing of sun : : ees : ; 5S, 9? Oi! 18. Z Sun to Corcovado . : : i 3 3 : f 120 45 Z Corcovado to building . : ea oe ; : ; 83 8 True bearing of building : : 5 c 5 SINS 53 23) We Observations of the Sun, made January 23d, 1866, to determine the true bearing of the object used as an azimuth mark in swinging the ship at Monte Video, Uruguay. : Near sunset, when the true zenith distance of the sun was about 90°, the angle between its nearest limb and the Light-house on the Mount, on the west side of the harbor, was measured. The uncor- rected reading of the sextant was 69° 40’, and the sun was to the left of the Light-house. 2 69° 40! Pe) BAS! a qo iy ) —iIg 19 S + 16 c 70 13 True bearing of sun : ‘ : 5 5 0 . S. 66° 13’ W. Z Sun to Light-house . 5 5 : 5 5 E 3 7O 13 Z Hillock to Light-house . é ‘ i = 34 18 True bearing of hillock . 0 3 : : ‘ 3 ING G7 Re We Observations of the Sun, made February oth, 1866, to determine the true bearing of the object used as an azimuth mark in swinging the ship at Sandy Point, in the Straits of Magellan. OE gee ILg° 15 15 19 : 32 I6 40 42 7 9 15 19 Q un 2 Chronometer slow © 12 48 ra) . i ti t = i 3O Ss +- 16 Apparent time Ona e 1A 8 t — 41° 36’ 4 50 32 : — 14 37 r ae == 5G MUL a 50° 31 M if — 19 14 b 89 34 o— 33 Bi Cc 130 54 True bearing of sun ; : ‘ : ‘ 6 tg ING BO” Bey 13% Z Mount St. Felipe to sun . : . & ‘ 0 5 Re) BZ True bearing of Mount St. Felipe . 5 o - Bh of adi WING MAGNETIC OBSERVATIONS. dl Observations of the Sun, made April 2d, 1866, to determine the true bearing of the object used as an azimuth mark in swinging the ship at Valparaiso, Chile. EE to? is* ZIo; 20) II 20 35 12 10 42 de ha Ln 2 Q Ilo 32 Chronometer slow © 19) 25 w + 17 T — See Ss — Apparent time Ii 7 ga ¢ IIo 49 t 79° 16 5 83 52 C) Be oe r — 8 o 33 2 a 83 44 M + 25 40 é nearly go g—M — 58 42 G 110 656 True bearing of sun : : : - : ° . N. 79° 49’ W. Z Sun to Point . 4 : ‘ 3 5 3 : 4 110 56 True bearing of Point . r : ; ae ow) CRE ise ey, Observations of the Sun, made April 27th, 1866, to determine the true bearing of the object used as an azimuth mark in swinging the ship at Callao, Peru. ah om 205 100° 50! 25520 55 on ES) TOL,» pL Sh if | ete Q 100 55 Chronometer fast One Tks on o SLY tT + Fe CG) S = Apparent time Gunn ounso c Iol 12 t — 76° 357 i 80 12 65 ioe ye r —_— ? i a So) 17 M + 46 44 6 nearly go o—M — 58 47 C IOl 21 True bearing of sun : : ; : é ‘ = IN Be Eloy Z Sun to flagstaff : : - : 2 : C ee TO Tea Z Flagstaff to Light-house. ; : : : A . 88 34 True bearing of Light-house . : é : : 5 BE eke) CIE Observations of the Sun, made May 13th, 1866, to determine the true bearing of the object used as an azimuth mark in swinging the ship in Panama Bay, New Granada. G27 Paes 86° 56’ 18 15 58 die any 4) Q 86 57 Chronometer fast ojPeeiey ty, o + 17 t ob 32088 5 = Apparent time(P.M.) he pi ats a 87 14 z go° 19’ ia 86 54 a 13) 3 te — 14 % 8 55 a 86 40 MM Sos é nearly go o¢—M —=) $0.) 85 C- 86 14 By REPORT ON True bearing of sun : é ; : : . . N. 71° 49’ W. Z Peaktosun . ‘ t : 2 3 6 5 : 87 14 True bearing of Peak . ‘ P 6 : : 2 S520) 57 We Observations to determine the true bearing of the object used as an azimuth mark in swinging the ship im the harbor of Acapulco, Mexico. When determining the magnetic declination with the portable declinometer, on May 30th, 1866, an observation of the sun with the theodolite gave N. 6° 22’ E. as the true bearing of the gate of Fort St. Diego from the shore station. We then have True bearing from station to Fort . 5 6 : . N. 6° 22’ EL Z Monadnock to Fort 0 : 3 . ; : 0 26 54 True bearing from station to Monadnock Os . N. 20 32 W. True bearing from Monadnock to station : 5 PSwzoe 32’ E. Z Clump to station . : c . : : 9 , STAs True bearing of clump . i - 3 : - N.7t 43 E. Observations of the Sun, made June oth, 1866, to determine the true bearing of the object used as an azimuth mark in swinging the ship in Magdalena Bay, Lower California. Owing to a combination of unfortunate circumstances, the only available method of determining a true bearing was by observing with the solar compass, set up on the quarterdeck of the ship. In that way I found True bearing of Peak . : . 5 : . 5 Sb AG? Gyo! JBp which can only be considered as a near approximation to the truth. Observations of the Sun, made June 23d, 1866, to determine the true bearing of the olject used as an azimuth mark in swinging the ship at San Francisco, California. icin Wp 92° 22 6 52 39 7 55 43 Te 7 © Ax Q 25) Chronometer fast QO BB 12 @ + 17 v — 1 SI S — Apparent time qo Be c 92 52 t Set ee ety g 64 8 ) 23 26 r — 2 co By AS) a 64 6 M ~ 58 30 b 89 51 o—M — 20 42 Cc 93 16 True bearing of sun 5 j 3 : : : . N. 79° 26’ E. Z Red Rock to sun . a 5 x , : . 3 93 16 True bearing of Red Rock . 4 3 : : aN ta SOMWe The following triangulation was made for the purpose of determining the geo- graphical position of some points in and about Ceara, Brazil. The angles were observed on December 14th, 15th, and 16th, 1865. Those between the Powhattan, beth MAGNETIC OBSERVATIONS. 33 Monadnock, and Custom-house were not measured simultaneously, and as the two ships were riding at anchor with a considerable amount of chain out, it is probable that they shifted their positions after the angle at the Powhattan was measured, and before the angles at the Monadnock and Custom-house were taken. ‘This will account for the excess of the sum of the three angles over 180°. In the accompanying sketch the different points are designated as follows: A = Point Macoripie Light-house. ; B = Northeast corner of Custom-house on the wharf. C =U.S. Iron-clad Monadnock. D = U.S. Sloop of War Powhattan. £ = most southern of the two steeples on the Church of the Conception. ’ = most southern of the two steeples on St. Joseph’s Church. M= Magnetic and Astronomical Station of December 13th and 14th. a aeeSae eae Cc ae Scale: 1 inch = 4000 feet. )M \ \ Ne one AS x E ¥F The observed angles were as follows: Angles at B. Angles at C. Angles at D. NGA ior ot D to A = 36° 10! Ato B — 05> ZF’ PDTONG) —=2 O47 Dios — 71 ai4 Bito C= 25 13 LEV) (GS Ge eo: Bto = 42 28 Ato C=t26 49 EoG ten, G Bt #=15 40 £toF= 52 15 AtoH=95 6 From these we obtain the following corrected Angles at B. Angles at C. Angles at D. towel 195° Li" Dto B= 740° 58 “tc = tor 36) Bitof=52 9 DtoA=36 14 Bon — ane RONG — 7a) | 14. AtoB=34 44 CtoD=84 5 Bto#H=15 40 Dito A= 55 20 Eto F=26 48 5 March, 1872, 34 REPORT ON The Powhattan fired a salute, and, from the mean of seven observations, the interval between the flash and report, noted at B, was 6.55 seconds. External thermometer 86°. Hence the distance from B to D was 7526 feet. Distance from B to JJ = 200 feet. Azimuth from Ito A = N. 75° 38’ E. Angle A M B= 128° 57. From these data we find the distances between the several points as follows: A D = 15814 feet. ‘CE = 4355 feet. BE = 1443 feet. AC = 21491 “ ; BC = 3358 “ C€D—=T7919 “* AB =18826 “* BF=2516 “ CF = 3568 << AM= 18702 “ Angle BA M=0° 28’ | Angle 4A MB=128° 57) | Angle 4 BA=50° 35’ Azimuth from A7to A =N. 75° 38’ E. Azimuth from Bto H=S. 8° 43’ E. « Btod=N.76 6 E. “s “ Bto fF =S. 43 26 W. Assuming the position of M to be ILati, 3° ag’ B6)".@ GS: Long. 2" 34" 6%.0o W. we get finally Station. Latitude. Longitude. B QO ale! 578 S. 2 aA) 68 We EE 2 AVL 12.0) 234507 LF 3 44 15-9 2 34 7-25 A 3 43 13-3 2 33 54-10 For convenience of reference the results of the observations contained in this section, together with the chronometer comparisons made during the cruise, are here collected and appended. Observed Latitudes. Name of station. Latitude. Fort Christian, St. Thomas . : j é : 18° 20’ o” N. Isle Royal, Salute Islands ; : . : . 5 17 29 N. Magnetic Station, Ceara, Bev 2 : 3 43 59 S. Custom-house, £ rinks : g 4g BS Ss Church of the Conception, Ceara, Brazil A ° BAA za: St. Joseph’s Church, : 6 a 3 44 16 S. Point Macoripie Light- -house, ‘‘ sats . 0 8 43 8B MAGNETIC OBSERVATIONS. 35 Lrrors of Pocket Chronometer, Fletcher, No. 906. Error on Local Error on GreenwichDate.penon: Mean Time. Mean Time. Portsmouth, Va. October 29, 1865 of 4™ 4r®.x fast 5" o” 28°.7 slow Portsmouth, Va. eS «sg fs Ar AOGE. 4 s5 0 29.7 *§ St. Thomas November 13, ‘¢ © 40 43.6 slow OF 26s eees Isle Royal . fs Day te Tego (ros4 «6° @ 30.8 < Ceara December 14, ‘‘ Zz OW nas he 66 5 Om eG. Spaese Pernambuco OC Bigneees 220 aAc Sine A 5Gs stato Bahia. ee By mens 2. 228 46:8 §€ Ge biyeae acs Bahia. es 20, 5 Ce GAPS EIKO). GO Oe STOLh ee Rio Janeiro January 9, 1866 2 3 38.4 * RO’ BR IOMENcee Rio Janeiro es «¢ ac 2 eeguesaia!. 56) Tony «<6 Monte Video ve ES, ne Cun) 277.008 | ROms227 G0. 5 Monte Video ee DAT ee Th eee 20. nen BOe exo s4) ase Sandy Point Hebrilanye on) °S Oo} “Hah a48in 8 BOR a2geqn. (°° Valparaiso . : c : . | March 2, mee OF OQ) AGr4a0. 56, a7.4) £8 Valparaiso . : < : ; do 205 Ou ZOLs mine On eOzGh ke Valparaiso . April a Bae O12 3a OF wQ.OMmite Valparaiso . : é : : ee eee On FOpn2330) wie Am GON aol Omics Valparaiso . : ; : Sal) ace i45 On PLE Petey as Ae AE AR eee Callao = : : : sf As Onlin 903 r5 fast GH) anda) OS Payta. May Os On 20) Amore. Gi Oct 4 Panama : fe TAs sé On 26) 16,9) *5 ALS) 44tou** Acapulco . z GO SO ae Ie Aro g2se. «6 4 58 TDG ee Magdalena Bay . June a 2 ‘308 Asa. SE on TOLGnae San Diego . Oe TS ae 2 sOM zene 6 Ae <5Se. 20r Tens This chronometer (Fletcher, 906) was habitually carried in my pocket. It was accidentally allowed to run down on the night of December 17th and 18th, 1865, and after remaining stopped twelve hours was wound and compared. Some time between 5" P.M. of April 13th and 3" P.M. of April 14th, 1866, it stopped for about 1™ 37%, but started again of itself. On June 20th, 1866, when its face showed 6" 45" P.M. it stopped without any apparent cause, and, as it would not run again, it became useless. In observing at San Francisco the box chronometer T. 8. and J. D. Negus, Ne. 1287 was used. ‘The observations on June 26th, 1866, showed it to be 8" 13™ 88.2 fast of local mean time; and 0' 3" 45°.6 fast of Greenwich mean time. 36 REPORT ON Chronometer Comparisons. D Fletcher, T.S. and J. D. Negus, | T. S. and J. D. Negus, aie 906. 1317. 1287. October 29; 1865 .. . 7 397 565.8 A. M. 125 44™ 08.0 October 29, ‘“ GR Me 2 28 56.0P.M 7d $3 @© October 31, “‘ Segoe Oe |e Tiel Se deanna 5 13 O© November 3, ‘‘ Oo A it BR.) 86 9 22 0.0 November 13, ‘‘ Sa ach 8 2t 4.8A.M I 26 0.0 November 13, ‘‘ suas |) ell ties Aer mete aimee eaatray = I 28 0.0 12 16™ 2335 November17, ‘‘ 72 18 AG.@ a4 C6 November 28, ‘“‘ 6 55 26.8 % iB 2 Oo November 28, ‘‘ 6 56 5653) << ates aid _ it 5O ©:© November 28, ‘‘ BR 86) Gad 12, Wil, 7 AS Os December 14, ‘‘ 6 29 23.0 A. M. II 36 0.0 December 14, “ 6 2 1.8 F Ui 8 O©. December 14, ‘“‘ TA AR BA.8 IP, Il, 5 50 0.0 December 16, ‘‘ 8 54 16.0 A. M. 2 i Co@- December 16, <“‘ 8 56 5.2 % I 51 0.0 December 18, ‘“ 9 44 42.8 P. M. 47 0.0 December 23, “‘ 8 FF 28.6 A. INL I IO 0.0 December 23, ‘‘ 8 & game 06 oi. .0.40 I2 59 0.0 December 29, ‘“‘ @ 27 ko.23 II 26 0.0 December 29, ‘‘ O 24 @@ % Ay ae ee II I5 0.0 January 9, 1866 6 A gig II 50 0.0 January On on © AG Agim Ee II 38 0.0 January 24, “‘ mA Ast Al) JP. IMI, 5 46 0.0 January 24, “‘ 1m} Alt Bea OY ake aes BB Cro April rae, “6 A i) BAA 8 9 29 0.0 May ee Ir 34 26.4A. M. 4 49 0.0 May PA iy 12 2 409.6 P. M. 5 18 Co May Bovine i 5S 13.8 As ML 5 1a ©) June Bute os 6 28 24.8 P. M. II 46 0.0 June WB, 12 o 46.8 A. M. 5 10 Oo June PA Aaa eal kPa CERN | (Cats Bey te aon) 6 34 0.0 P.M. 6 17 0.2 Table showing the True Bearings of the various objects used as azimuth marks in swinging the U.S. Lron-clad Monadnock during her cruise from Philadelphia to San Francisco in 1865 and 1866. Station. : True bearing. z Hampton Roads, Va. . S. 10° 34’ W St. Thomas : : 6 Sh Qu Qs Isle Royal, Salute Islands . S. 10 54 W Ceara ‘ : Ne S2n a7 et Bahia N. 81 57 W. Rio Janeiro N,Q a8 Wo Monte Video N. 77 52 W. Sandy Point Se 9 ue We Valparaiso IN Qt 1p Callao S. 83 21 W. Panama Bay . Sb 2 87 Ve Acapulco . : 5 N. 71 43 E. . Magdalena Bay . : 5 0 S. 46 30 E. San Francisco Bay . : : a IN, 72 SO Wo MAGNETIC OBSERVATIONS. . 37 SECTION IV. OBSERVATIONS ON TERRESTRIAL MAGNETISM. Tue observations of magnetic declination and force were made by means of the same instruments—a portable declinometer, and a transit theodolite. The Declinometer, kindly lent by the U.S. Coast Survey, and marked D. 22, was originally constructed by Jones, of London, but had been altered in many particulars so as to make it more convenient for field use. It was provided with two collimator magnets which were hollow cylinders of steel, each 0.70 of an inch in external diameter, and 0.58 of an inch in internal diameter. One of them, marked C. 32, was 3.92 inches long; while the other, marked S. 8, was 3.25 inches long. Each of these magnets carried in its south end a lens; and in its north end, at the solar focus of the lens just mentioned, a piece of plane glass on which was cut a scale of equal parts containing one hundred and seventy divisions, each division being equal to 0.00255 of an inch. Both magnets were provided with light sliding brass rings which were intended to be used for keeping them horizontal under great changes of magnetic declination, but the slight play which the magnets had in the stirrup was found quite sufficient for that purpose, and the rings were never employed. The same suspension was used during the whole of the observations. It consisted originally of six parallel fibres of unspun silk, each about nine inches long; but at Callao one of the fibres was accidentally broken, and after that the remaining five were used. The torsion circle, which formed part of the suspension apparatus, was 0.88 of an inch in diameter, divided to every three degrees, and read by means of a vernier to single degrees, The Transit Theodolite, which perhaps might be more correctly called an altitude and azimuth instrument, was provided with a horizontal and a vertical circle, each five inches in diameter, and each reading by means of two opposite verniers to thirty seconds. The telescope had an object-glass with a clear aperture of one inch, and a focal length of about nine inches, It was provided with two eye-picces; a direct one magnifying about twenty times, which was employed in almost all the observations; and a diagonal one of lower power, which was sometimes used for objects