box: 5 cm x 24.4 cm x 15.5 cm; 1 31/32 in x 9 19/32 in x 6 3/32 in
United States: New York
This German silver L-shaped bar has a pivoting rectangular piece underneath the end of its short leg. A small cylindrical handle and a tracer point are at the end of the long leg. A measuring wheel at the vertex is numbered from 0 to 10 to 0. The divisions are engine-divided and thus finely made.
The instrument fits into a crudely made wooden case. The lid of the case has two German silver tracks, two German silver clamps for holding paper, and a German silver pivoting arm that may be used to secure one of the clamps. The rectangular piece on the instrument slides into one of the tracks so that the tracer point can be moved along a curve drawn on paper in the holders. The measuring wheel thus found the area under the curve, which was produced by a steam engine indicator.
John Coffin of Syracuse, N.Y., applied for a patent on this variation of a planimeter in July 1881. Although several companies subsequently manufactured forms of Coffin's planimeter, this example resembles none of the production models identified by collector David R. Green or depicted by N. Hawkins or James Ambrose Moyer. However, this instrument is very similar to Coffin's patent drawings. This similarity, the crude construction of the case, and the absence of maker signatures and identifying marks suggest that this version of Coffin's planimeter was not made in large quantities. Perhaps it was even a patent model, since Coffin did submit one with his application. The Museum owns patent models from as late as 1910, and this object came to the Smithsonian some time before it was found in the collections in 1964. According to Janssen, no list was made of the 15,000 models received in 1926, although all of the 1,000 models collected in 1908 were recorded and accessioned. There is no Patent Office tag on this instrument.
Coffin announced in his patent specification that he would soon move to Chicago, and there is no record of his activities after 1882. Compare this object to 1987.0107.03, MA.323705, and MA.323706.
References: John Coffin, "Averageometer, or Instrument for Measuring the Average Breadth of Irregular Planes" (U.S. Patent 258,993 issued June 6, 1882); N. Hawkins, <i>Hawkins' Indicator Catechism</i> (New York: Theo. Audel & Co., 1903), 140–142; James Ambrose Moyer, <i>Power Plant Testing</i> (New York: McGraw-Hill, 1911), 73–78; David R. Green, "Coffin Planimeters," <i>The Planimeter Vault</i>, June 16, 2008, http://www.planimetervault.com/coffin.html; Barbara Suit Janssen, <i>Patent Models Index: Guide to the Collections of the National Museum of American History</i> (Washington, D.C.: Smithsonian Institution Scholarly Press, 2010), i:viii–ix, 150.