Wetli & Starke No. 44 Wheel and Disc Planimeter

In the 1810s and 1820s, three Europeans independently invented the planimeter, an instrument for finding the area bounded by a closed curve. The third of these devices, by the Swiss Johannes Oppikofer, was the first to be commercially manufactured, by Ernst of Paris in 1836. In 1849 Kaspar Wetli, a Swiss engineer and railway designer, received an Austrian patent for replacing the cone used by Ernst with a wheel and disc. This increased the accuracy with which the instrument traced a curve when the surface being measured was uneven. Georg Christoph Starke made improvements to the device, which was described by Simon Stampfer in 1850. The planimeter won a prize at the 1851 Crystal Palace Exhibition.
Starke's workshop in Vienna manufactured at least 100 of the instruments over a ten-year period. (The Science Museum in London estimates the date for serial number 103 as around 1860.) This example is serial number 44. Hermann, Adolf, and Robert Schlagintweit, German brothers and explorers, took this instrument on their travels in India and the Himalayas between 1854 and 1857. They were sponsored by the East India Company on the recommendation of Alexander von Humboldt.
The planimeter is in a large wooden case that has two spools of replacement wire in the lid. The instrument has a rectangular brass base. A brass wheel mounted on the base is divided by degrees and marked by tens from 0 to 90 three times. A wheel inside this wheel is marked from 0 to 110. The larger wheel is attached by a metal shaft to a metal wheel. When the metal wheel turns, measurements are recorded with a pointer and the smaller wheel.
A second part of the instrument has a tracer arm with brass and ivory handles at one end. When the handle is moved, a wire running the length of the arm turns a porcelain disc. This whole assembly slides perpendicularly onto brass rods on the base of the first part of the instrument. Thus, the arm rotates the porcelain disc, which rotates the metal wheel, which triggers the recording pointer and wheels. The arm is engraved: Patent von Wetli & Starke No 44. The arm is also engraved: Schlagintweit Ho.
The case also holds two large points, which may be meant to serve as styluses but which do not fit the instrument; a brass calibration disc engraved with two circles, marked 49.88 c.m. and 35.63.c.m.; three brass tacks; and a key on a blue ribbon. The instrument was received with documentation (1986.0633.02 and 1986.0633.03).
References: Louis F. Drummeter Jr., "Starke & Kammerer in San Francisco," Rittenhouse 5 (1990): 25–32; Peggy Aldrich Kidwell, "Planimeter," in Instruments of Science: An Historical Encyclopedia, ed. Robert Bud and Deborah Jean Warner (London: Garland Publishing, 1998), 467–469; Charles Care, "Illustrating the History of the Planimeter" (Undergraduate 3rd Year Project, University of Warwick, 2004), 8, 29–37; accession file.
Currently not on view
Object Name
date made
Wetli, Casper
Starke, Christoph
Physical Description
brass (overall material)
metal (overall material)
ivory (overall material)
wood (overall material)
case: 17 cm x 50.2 cm x 29 cm; 6 11/16 in x 19 3/4 in x 11 13/32 in
place made
Österreich: Wien, Vienna
ID Number
catalog number
accession number
Science & Mathematics
Measuring & Mapping
Exploration and Discovery
See more items in
Medicine and Science: Mathematics
Data Source
National Museum of American History, Kenneth E. Behring Center
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