DlAMAGNETIC CONSTANTS OF BlSMUTH AND CALC-SPAR 193 



these various equations give the complete solution of the problem of 

 finding the various coefficients of magnetization. 



PART II. BY W. W. JACQUES 



In the foregoing part of this paper there have been deduced mathe- 

 matical expressions for the constants He and ~k' both for bismuth and 

 for calc-spar crystals. In these expressions it is necessary to substitute 

 certain quantities obtained by a series of experiments, and it is the 

 purpose of the remaining portion of the paper to describe briefly the 

 way in which these quantities were obtained. 



These experiments are naturally divided into two parts. First, the 

 exploration of the small magnetic field between the two poles of the 

 electromagnet, and second, the determination of the time of swing and 

 certain other constants relating to little bars of the substances experi- 

 mented upon when suspended in this field. 



In order to insure the constancy of the magnetic field, a galvano- 

 meter and variable resistance were inserted in the circuit through 

 which the magnetizing current circulated. This space between the 

 poles of the electromagnet in which the experiments were performed 

 was a little larger than a hen's egg. 



The method of exploring this field was as follows : In the line join- 

 ing the centre of the two poles was placed a little brass rod, along 

 which a very small coil of fine wire was made to slide. To this rod 

 were fixed two little set-screws to regulate the distance through which 

 the coil could be moved. Starting now always from the centre, the 

 coil was moved successively through distances a, & and c, and the cor- 

 responding deflections of a delicate mirror galvanometer contained in 

 the circuit were noted. To each of these deflections was added the 

 deflection due to quickly pulling the coil away from the centre to a 

 distance such that the magnetic potential was negligibly small. Of 

 course, experiments were made on both sides of the centre of the field 

 in order to eliminate any want of symmetry, and the distances through 

 which the coil moved were all carefully measured with a dividing engine. 



In order to reduce the deflections of the galvanometer to absolute 

 13 



