114 Mr. J. E. Moore on a Continuous and 



netometer helix. The compensating coil should be so con- 

 nected in series with the magnetizing coil as to give an 

 opposing magnetic effect at the I-magnetometer helix, and by 

 keeping its plane horizontal, and its centre in the vertical 

 line of suspension of the magnetometer system, be adjusted in 

 position until the joint magnetic effect of the two coils at the 

 I-magnetometer helix is zero, for all strengths of current 

 through them. 



§ 6. The instrument, having thus been set up and adjusted 

 and the adjustments tested, is ready to be used for the 

 measurement of energy-losses in iron magnetized by either 

 direct or alternating currents. If the losses in iron magne- 

 tized by continuous currents are to be measured, a current of 

 two-tenths of an ampere from some independent battery (a 

 single cell of storage-battery answers very well) is passed 

 through the helices of the magnetometer system, and kept 

 constant throughout an experiment. The intersection of the 

 cross-hairs in the beam of light reflected upon the recording 

 screen by one of the mirrors carried by the I-magnetometer 

 helix, is taken as the centre of a system of vertical-horizontal 

 rectangular coordinates. The sample is then placed in the 

 magnetizing coil, which, after being properly connected in 

 series with the compensating coil, the H-defleeting coils of 

 the instrument, a regulating resistance, and a source of con- 

 tinuous current, has the magnetizing current through it 

 increased from zero to the maximum value required to produce 

 the desired maximum degree of magnetization, reduced to 

 zero, reversed, the same operation performed in the opposite 

 sense, and the cycle completed by returning finally to the first 

 maximum. The point of intersection of the cross-hairs on the 

 screen will be displaced for every different value of the mag- 

 netizing current, a distance from each of the coordinate axes 

 previously drawn, proportional respectively to the magne- 

 tizing force acting on the sample and the intensity of 

 magnetization of the sample. Hence by marking down on 

 the screen the point of intersection of the cross-hairs in the 

 reflected beam of light, for any desired number of values of 

 the magnetizing current throughout the cycle of magnetiza- 

 tion, we have an accurate outline of the magnetization curve 

 for the sample, or, as it is frequently called, the " hysteresis " 

 curve. By properly varying the magnetizing current, loops 

 can be traced to any part of the hysteresis curve, or a com- 

 plete set of graded cycles obtained without removing the 

 sample. 



In measuring the losses in iron magnetized by an alter- 

 nating current, an intermittent current of a mean value of 



