Feedback Mechanisms in the Historical Collections of the National Museum of History and Technology

Abstract

Among the seemingly endless variety of machinery that might be listed under the heading <i>automatic control</i>, feedback mechanisms stand out as a distinct group because, although differing widely in outward appearance, they all function according to a single principle. The significance of the principle of feedback is all the greater as it is not limited to technology. Since 1948, when Norbert Wiener adopted it as one of the unifying concepts of the new science of <i>cybernetics</i>, it has come to be regarded as an invaluable tool in such diverse disciplines as biology, economics, and sociology. The interdisciplinary validity, for which the concept is admired, has been anticipated in technology at a much earlier period, when feedback was employed to solve problems of control, for example, in the mechanical, hydraulic, thermal, and electrical media. It might be of interest therefore to outline the history of feedback control by means of cataloging—systematically and in chronological order—the historical feedback devices contained in the collections of one of the world's great technological museums, the National Museum of History and Technology of the Smithsonian Institution. This catalog is limited to feedback mechanisms; other forms of automatic control, for example open-loop and programmed control, are disregarded without further explanation. The material to be described has definite boundaries also in space and time. In space, it is limited to the collections of the Smithsonian Institution's National Museum of History and Technology, collections which are partly exhibited and partly stored in various storage spaces; in time, it is limited to items that can be described, at least by lenient standards, as historical. How old must an item be to qualify? Objects that are being mass-produced and commercially marketed at the present are clearly inadmissible. On the other hand, certain developments—such as in the field of computers—may have to be considered historical even if they have occurred relatively recently. A cutoff date convenient for our purposes then seems to be the end of World War II, a date we will disregard, however, when appropriate. In an effort to make visible the more important lines of development of historical feedback devices, the material is presented in the form of a continuous narrative. This has led to an arrangement which is pragmatic rather than strictly systematic. Sometimes feedback devices are classified according to the controlled variable (e.g., speed, pressure, temperature); sometimes it has been more expedient to list them under the branch of technology where they were employed (e.g., automotive or textile). The necessary cross-references will be provided by the index. To describe individual objects, we have to consider two kinds of information: First, information concerning its external history has been presented, at least in concise form, as far as available, but the scope of this catalog did not permit the additional research required to close numerous gaps. Second, complicated technical objects such as we deal with here require technical description. Readers who may feel that too much space is devoted to purely technical matters should take into account that the historical significance of the objects cataloged here lies precisely in the technological ideas represented by them. The sources used and references to additional material have been indicated as usual in footnotes. Further information may be found at two general sources. One is the archives of the individual divisions of the Museum. For access to these, researchers should consult the respective curators directly. The other concerns the patent models which form a considerable part of this material. The patented inventions are described in detail in the patent specifications, and further material may be found in the case files of the United States Patent Office and the National Archives. The imaginative reader may miss in this catalog some items that he would have expected to find. This may be due to any one of three reasons: his definition of feedback may differ from the author's; the item may have been accidentally overlooked; or the item may actually not be represented in the collection. With regard to definition, the following practice has been followed. At the start, feedback was defined once and for all; thereafter only devices thus defined were accepted, others were disregarded without discussion. In a few cases, where whole groups of relevant objects were excluded for special reasons, as in the cases of safety valves, float-feed carburetors, or electronic devices, this was explained at the appropriate places. Second, feedback devices are rendered elusive by the interdisciplinary nature of the concept. Feedback is employed in many disguises, and it is represented in practically all divisions of the Museum. In spite of a serious effort to make this catalog exhaustive, it is only too possible that one or another item may have escaped the cataloging. Finally, the collection itself must not be expected to be complete. Feedback devices usually are inconspicuously attached to some larger machine or process which they have the function to regulate. Having rarely been collected for their own sake, they are represented unevenly. Our collection, for example, contains more than a hundred speed governors but only a few historical temperature controllers. All items listed have actually been identified in the collections. Each individual object is identified by two numbers, the catalog number (NMHT) and the accession number. The <i>catalog numbers</i> are assigned individually to specimens by each particular Museum division according to systems which vary between different divisions. The <i>accession numbers</i> indicate the accession files in the Registrar's office and are uniform for all of the Museum. The accession files contain all correspondence and other documents relating to the transaction by which the specimen reached the Museum, often containing valuable detailed information. A single accession number may refer to more than one object. As a help in finding the objects cataloged herein, we have included a <i>Location Guide</i> at the back of the book.