Coffin Planimeter Arm Signed by Ashcroft Manufacturing Company, No. 830
date: label: date made
content: 1882-1910
name: label: maker
content: Ashcroft Mfg. Co.
notes: label: Description
content: This German silver instrument is a curved bar with a short arm, on which a short cylindrical weight is placed, and a longer arm, to which a tracer point is screwed. The middle of the bar has a thin cross-rod, on which a measuring wheel rotates against a wedge-shaped vernier. The wheel is numbered from 0 to 14, with each unit divided into five parts. The bar is marked: THE ASHCROFT MFG. CO. (/) — SOLE MANUFACTURERS. — (/) COFFIN'S PAT. JUNE 6. 1882. The underside of the bar is marked: No. 830. The serial number suggests this object predates 1987.0107.03. Compare also to MA.323708 and MA.323706.
label: Description
content: A wooden case covered with dark brown leather is lined with purple silk and velvet. The top of the case is marked: MADE BY (/) THE ASHCROFT MANF'G CO. (/) NEW YORK & BRIDGEPORT.
label: Description
content: John Coffin of Syracuse, N.Y., applied for a patent on this variation on a planimeter in July 1881. He designed his "averageometer" to calculate areas in diagrams of work performed by steam engines. The Ashcroft Manufacturing Company of New York City and Bridgeport, Conn., was the first of several American firms to make the device.
label: Description
content: Ashcroft, best known for making pressure gauges for steam engines, often sold the arm for Coffin's planimeter separately from its base, as in this example. In 1910, Frederick C. Blanchard, Ernest B. Crocker, and Philip G. Darling, who all probably worked for Ashcroft, patented an improvement to Coffin's planimeter so that it could be clamped in place. The planimeters made by Ashcroft after 1910 utilized this improvement, so this example was made between 1882 and 1910.
label: Description
content: The instrument was received at the Smithsonian in 1964.
label: Description
content: References: John Coffin, "Averageometer, or Instrument for Measuring the Average Breadth of Irregular Planes" (U.S. Patent 258,993 issued June 6, 1882); F. C. Blanchard, E. B. Crocker, and P. G. Darling, "Planimeter" (U.S. Patent 961,836 issued June 21, 1910); David R. Green, "Coffin Planimeters," June 16, 2008, http://www.planimetervault.com/coffin.html; N. Hawkins, <i>Hawkins' Indicator Catechism</i> (New York: Theo. Audel & Co., 1903), 140–142.
label: Location
content: Currently not on view
place: label: place made
content: United States: New York, New York City
topic: label: Subject
content: Mathematics
label: Subject
content: Engineering
setName: label: See more items in
content: Medicine and Science: Mathematics
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content: Planimeters
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content: Science & Mathematics
creditLine: label: Credit Line
content: Gift of New York University
dataSource: label: Data Source
content: National Museum of American History
identifier: label: ID Number
content: MA.323705
label: catalog number
content: 323705
label: accession number
content: 252307
objectType: label: Object Name
content: planimeter
physicalDescription: label: Physical Description
content: german silver (overall material)
label: Physical Description
content: wood (overall material)
label: Physical Description
content: leather (overall material)
label: Physical Description
content: cloth (overall material)
label: Measurements
content: case: 3 cm x 18 cm x 7.4 cm; 1 3/16 in x 7 3/32 in x 2 29/32 in