Ohm

Unit of electrical resistance; equal to 10o C.G.S. electromagnetic units. The megohm is one million ohms: the microhm is one millionth of an ohm. The standard ohm, constructed by the Electrical Standards Committee of the British A ociation, and intended to be 10o C.G.S. electromagnetic units of resistance. was found by Lord Rayleigh to be 1.3 per cent too small. The International Electrical Congre at its final se ion in Paris 1884 defined the ohm to be equal to the resistance of a column of mercury 1 square millimeter in cro section and 106 centimeters long. This ohm is known as the Congre or the Legal ohm. The average of later experiments of Prof. Rowland show the length of this mercury column to be probably 106.24 centimeters; so that the Congre ohm is too small by tabulated as follows: IMG:content-1641.jpg:[merged small][ocr errors][ocr errors] 1 theoretical ohm=10° C.G.S.E.M. units=106.24 cm., mer. col. B.A. unit-.9889 Congre ohms=104.93 cm., Siemen's unit-.9540 B. A. units -100 cm., IMG:content-1642.jpg:[ocr errors] IMG:content-1643.jpg:[ocr errors]