Amsler is also credited with conceiving a design for a planimeter that restricted the movement of the end of the tracer arm opposite the tracer point to a straight line. The collections suggest that Americans were particularly interested in further developing linear planimeters, with examples patented by John Coffin, Edward Jones Willis, and Frederick R. Williams. Another linear planimeter sold by an American company and an instrument that does not fit any of the categories of planimeters are also included on this page.
In 1875, Danish mathematician and cavalry officer Holger Prytz came up with a final form of planimeter—the hatchet planimeter. It simply consists of a rod with a tracer point at one end and a chisel edge at the other. As the tracer goes around the drawing, the chisel makes a zigzag path. The product of the length of the path and the length of the rod gives the area of the drawing. The result, though, is not as accurate as those provided by more complex forms of planimeters. At present, no examples of this instrument are known to be among the mathematics collections.
"Planimeters - Linear" showing 1 items.
- On August 18, 1902, Levi T. Snow of New Haven, Conn., filed a U.S. patent application for improvements to the planimeter invented in 1882 by John Coffin for measuring the area under curves drawn by the gauge on a steam engine. (See MA*323708, MA*323705, and 1987.0107.03.) For instance, Snow added a tube containing a set of scales for the pressures under which the diagrams were made. He assigned the patent to the John S. Bushnell Company of New York City, which manufactured and sold the instrument as "Bushnell's Improved Planimeter" and the "Bushnell-Coffin Planimeter."
- This Bushnell-Coffin planimeter consists of an aluminum base with four black rubber feet. Two aluminum rods are screwed to the base, with a movable indicator on one rod and a sliding tube marked with six sets of scales for pressures on the other rod. A rectangular support for the planimeter arm is bolted to the base at the left end of the rods. The serial number 303 is stamped next to this support.
- A smaller rectangular aluminum base slides between two bars on the right side of the larger base. Both bases have clamps for holding paper diagrams. The aluminum planimeter arm is a single curved bar. One end of the arm and a short cylindrical weight fit into a hole on the movable indicator. The other end of the arm has a tracer point that moves over the diagram held on the bases. A single bar near the weighted end of the arm has a brass vernier and a brass measuring wheel, which is numbered from 0 to 14, with each unit divided into five parts.
- A wooden case covered with black leather is lined with blue velvet. The top of the case is marked: Bushnell – Coffin Planimeter. The left end of the case is marked: A–5. The right side of the case is marked: M.E. LAB. (/) COFFIN. A flap inside the lid holds the smaller base and flips up, perhaps to store extra paper. A ribbon on the flap has an oval logo marked: AMERICAN * SCHAFFER & BUDENBERG. Inside the oval are a picture of a steam engine gauge and the words: BROOKLYN, N.Y.
- By 1916, the John S. Bushnell Company was making the Bushnell-Coffin Planimeter and the American Steam Gauge & Valve Manufacturing Company was selling it for $55.00. In 1923, American Steam Gauge, the Hohmann-Nelson Company, and the American division of the Schäffer & Budenberg Manufacturing Company merged to form American Schaeffer & Budenberg Corporation. The firm may have been purchased by Manning, Maxwell, and Moore in the late 1930s. The mechanical engineering laboratory of New York University owned this instrument.
- References: Levi T. Snow, "Planimeter" (U.S. Patent 718,166 issued January 13, 1903); David R. Green, "Coffin Planimeters," June 16, 2008, http://www.planimetervault.com/coffin.html; "The Bushnell Improved Coffin Planimeter," The Engineer's List 11, no. 11 (November 1902): 37–38; American Steam Gauge & Valve Manufacturing Co., Catalog No. 65 (Boston, 1916), 810; advertisement for the Bushnell-Coffin Planimeter, Power 49, no. 25 (June 24, 1919): 105; Barry Lee David, The Antique American Steam Gauge: A Collector's Guide (Mendham, N.J.: Astragal Press, 2003).
- Currently not on view
- date made
- 1923-ca 1937
- John S. Bushnell Company
- ID Number
- catalog number
- accession number
- Data Source
- National Museum of American History, Kenneth E. Behring Center