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arm, consult and instrument

PLANIM'ETER (from Lat. planum, level ground, plain + bLe r po v, metron, measure). An instrument for automatically measuring the areas of maps and plans. The first usable plan imeter seems to have been constructed in 1814 by a Bavarian engineer named Hermann (1785 18I1 ). This was followed by an ingenious device invented by a Swiss engineer, Opikoffer, in 1827, and perfected ten years later by Ernst of Paris. The next notable type was the polar plan imeter made by the firm of Amsler-Laffon of Sehaffhausen (1854) and known as Amsler's planimeter. This well-known instrument con sists of two arms hinged at one end, the outer end of one being a pointed support and that of the other a tracing pencil. The latter arm also hears a graduated cylinder which rolls on the paper, its axis being parallel to the arm. To obtain the area of a figure the instrument is moved bodily about the pointed support on the first arm, while the tracer of the other arm de scribes the perimeter of the area, and the gradu ated cylinder records the required area. Tins and the 'Wetlische Linearplanirneter,' manufac tured in Vienna, are the best planimeters now made. The mathematical principles involved

may be found in works on surveying. The best description of the Amsler planimeter is`given in Bauernfeind's Elemcntc der l'crtnessungskunde (7th ed., Stuttgart, 1890). Consult, also, Ams ler, Ucber die 111CChanische Bestimmung des Flachcninhalts (Schaffhausen, 1856). The latest improvements on the polar planimeter have been made by Hohmann and Coradi in their 'Priizi sions-Polarplanimeter.' and by Coradi in •his 'Kugel-Rollplanimeter,' on which consult Lorber, Zcitschrift fur Vermessungstresen (vols. viii. and xvii., Stuttgart, 1884, 1888), and Amsler Laffon, 'Planimeterkonstruktionen,' in the Zeit schrift fib. Instrumentankunde ( 4. Jahrg., 1884), and Des Monzentenplanimetcr (Zilrich, 1875). For the history of the subject, consult: Trunek, Dic Planimetcr; duet? Thcoric, Praxis nod Gc schichtc 1865) ; Bauernfeind, in Dingler's Polytcchnisches Journal (vol. cxxxvii.); and Fa varo, in the Allgemcinc Bauzeitung (1873).