E. B. Rosa and F. W. Grover 125 E. B. Rosa and F. W. Grover 153 C. W. Waidner and G. K. Burgess 189 On the Theory of the Matthews and the Russell-Léonard Photometers for the Measurement of Mean Spherical and Mean Hemispherical Intensi- THE ABSOLUTE MEASUREMENT OF INDUCTANCE." By EDWARD B. ROSA and FREDERICK W. GROVER. 1. METHODS OF MEASURING INDUCTANCE. Self inductance may be determined in absolute measure (that is, in terms of resistance and time) by the methods of Maxwell, Wien, or Rowland. The first named is complicated and scarcely capable of giving results of high accuracy. The other two methods are probably capable of yielding results of satisfactory accuracy, but so far as we know few results by these methods have been published, and none of a degree of accuracy equal to the results which have been obtained in the absolute measurement of a capacity. The most obvious method of directly determining the inductance of a coil, originally proposed by Joubert, consists in first determining the impedance of the coil and then calculating the inductance, after having found the ohmic resistance of the wire and the frequency of the current employed. Brew has given some determinations of inductance by this method, using a Cardew voltmeter, first in series with the inductive coil and second with the coil cut out. Knowing the resistance of the coil and of the instrument, and the frequency of the current, the inductance is calculated. The results on a single coil are given; they show considerable variations, as would be expected. Nothing is said of the wave form, although the formula employed presupposes a sine wave. Several variations of this method are described by Gray and Fleming. According to Gray, a noninductive resistance is placed in series with the coil whose inductance is to be measured, and an alternating current passed through both. By means of an electrometer, a A paper presented at the International Electrical Congress, St. Louis, 1904. Electrician: 25, p. 206; 1890. Absolute measurements: II, pt. II, p. 488. a Handbook for the Electrical Laboratory: Vol II, p. 205. |