Brown and O'Callaghan — The Rigidity of Nickel Wire. 101 



From the table and the curves it will be seen that for a direct longitu- 

 dinal field and given load on the wire the rigidity of nickel at first 

 increases and reaches a maximum in a field of about 26 units ; it then 

 decreases rapidly to a minimum, which occurs in a field of about 41 units. 

 It again increases up to its initial value in a field of about 77 units, and 

 continues to further increase, as far as our observations went, that is, up to 

 120 units. 



Fig. 1. — Upper Curve I). C. FieM. 



Lower Curve A. C. FielJ. (h 



50). 



For the alternating longitudinal magnetic fields of frequency 50 per 

 second, the curve follows the same general shape as with the direct field ; 

 but the first maximum is approximately half the value of the corresponding 

 maximum for the direct field, and occurs in a magnetic field of about 17 units, 

 whilst the minimum point is lower, and occurs in a field of about 38 units, 

 then rises to its original value in a field of about 103 units. If the values 

 in columns 3 and 5 of Table I (that ia, for frequencies 20 and 100 per second) 

 were plotted, the curves would be found to lie one above and one below the 

 curve for frequency 50 per second. 



One load only was tried in this part of the work, as the effect of increased 



