Alternating Current Magnetic Curve Tracer. 113 



I-magnetometer helix lies in the vertical axis of the suspended 

 system, and the torsion adjusted in the wires until the axis of 

 the helix is horizontal. The torsion-head of the instrument 

 is then turned until tbe axes of the magnetometer helices are 

 parallel to the planes of the H-deflecting coils. 



Upon one of the mirrors, carried by the I-magnetometer 

 helix, is projected a beam of light from some fixed source, which 

 after reflection is received upon a screen placed normally to 

 the helices in their undisturbed position. By means of cross- 

 hairs placed in the path of the incident beam of light, one is 

 enabled to mark on the screen the initial or zero position of 

 the magnetometer system, and to measure any subsequent 

 angular displacement of either or both of the magnetometer 

 helices. 



The sample to be tested (in the form of a long rod supplied 

 with the proper magnetizing coil) should be placed with its 

 axis in the vertical line of suspension of the magnetometer 

 system. This can be accomplished most conveniently by 

 clamping the sample and its magnetizing coil below the 

 support of the instrument. The sample and its magnetizing 

 coil should then be adjusted vertically, until the magnetic 

 action of the sample, for maximum intensity of magnetization, 

 produces the desired maximum vertical deflexion of the I- 

 magnetometer helix. A compensating coil of a few turns of 

 wire should then be adjusted so as to neutralize, at the I- 

 magnetometer helix, the magnetic action of the magnetizing 

 coil about the sample. 



The accuracy of the adjustments for horizontal displace- 

 ments can be tested by making the magnetometer helices 

 active, by means of a constant current of one or two tenths of 

 an ampere, and reversing an independent direct current 

 through the H-deflecting coils. This should give the mag- 

 netometer system equal horizontal displacements on either 

 side of the zero position, and, for various current-strengths, 

 the magnitude of these deflexions should be proportional to 

 the respective currents. 



The accuracy of the adjustments for vertical displacements 

 depends upon the setting of the sample to be tested (with its 

 magnetizing coil) and the balancing coil. This can be tested 

 before beginning an experiment by placing the magnetizing 

 coil (with the sample removed) in the position it will occupy 

 during an experiment, and reversing continuous currents of 

 various strengths through it. There should be no horizontal 

 displacements, and the vertical displacements, on either side 

 of the zero position, should be proportional to the respective 

 magnetic forces dne to the magnetizing coil, at the I-mag- 



PhiL Mag. S. 5. Vol. 41. No. 249. Feb. 1896. I 



