Effect of Stress on Magnetization. 



67 



one that had been used in our previous experiments, was 

 placed in its vertical position. The length and the constant 

 of the coil were respectively 40 cm. and 3926. A secondary- 

 coil was wound on a glass tube (external diameter 1*5 cm.), 

 consisting of 1246 turns of well insulated copper wire 

 (diameter = 0*56 mm.) in six layers, the length of the coil 

 being 14 cm. This secondary coil was fixed coaxially in the 

 magnetizing coil, so that the former might lie in a uniform 

 field excited by the latter. 



To compensate for the 

 induction due to the 

 magnetizing field alone, 

 a similar secondary coil 

 connected in series with 

 the above secondary coil 

 was inserted within 

 another coil equal to 

 and connected in series 



with the magnetizing 



© © 



coil, so that by sliding 

 the secondary within 

 the primary, the induc- 

 tion could be compen- 

 sated to any desired 

 degree. These two pairs 

 of coils were placed at 

 a sufficient distance from 

 each other to prevent 

 their mutual action. 

 The ballistic galvano- 

 meter for measuring the 

 induced current due to 

 the magnetization of the 

 specimen was drum - 

 shaped, with 0*8 12 

 resistance ; a mirror 

 with a. small magnet 

 was suspended in the 

 centre of the coil by a 

 spider thread. Its period 

 of oscillation was about 9 seconds. The galvanometer was 

 connected with the secondary circuit of the system and placed 

 at a distance of about 15 metres from the maonetizino; coil to 



© o 



avoid its direct action. The galvanometer was, however, 

 still disturbed when a strong current was switched on to the 

 magnetizing coil. To prevent this^ the compensating primary 



F 2 



