RESEARCHES OX MAGNETOSTRICTION. ;>(;<) 



It will be clear from the arrangement for compensation that not 

 only was the effect of magnetization on the magnetometer to a great 

 extent compensated, but the effect of rise of temperature due to the 

 magnetizing current was also provided for, since the auxiliary magnet 

 was enclosed in a similar brass tube and placed in the coil of the same 

 dimension and resistance. It is to be remarked that the compensation 

 was never exact, for although the ovoids or the rods were made of the 

 same material, there was some difference of quality as regards magnetiza- 

 tion. Thus the compensation, though exact in certain fields, was not ful- 

 filled throughout the whole range of fields ; nevertheless, the difference 

 was not very great, and we believe that the influence of the rise of tem- 

 perature or that of strain due to pressure will not have been so large as 

 to materially deteriorate the experimental results. In spite of this, care 

 was taken to keep the field during the experiment constant by watch- 

 ing the indication of the deci-ampere balance, by which the current was 

 measured ; further, it was generally possible to perfect the compensa- 

 tion for feeble change of current by slightly shifting the auxiliary 

 magnet or the coil. 



The horizontal component of the terrestrial magnetic force was 

 slightly affected by thus placing the coils very near the magnetometer, 

 and it became necessary to measure the period of vibration of the 

 magnetometer magnet by means of a chronograph, and to apply the 

 correction to the measured intensity of magnetization. 



The change in the intensity of magnetization due to the alteration 



ni volume is evidently nearly equal to —I . The diminution of 



volume will therefore produce increase of magnetization. It will be 

 seen that the correction due to the contraction of volume of the magnet 

 is of the same order as the change in magnetization wrought by com- 

 pression, from which the smallness of the effect can be easily judged. 



