Brown and O'Cali.aghan — The Rigidity of Nickel Wire. 103 



magnetic field and the vibration of the mirror, we were not able to measure 



fully the effects of transverse alternating magnetic fields on the rigidity, but 



an approximate set of readings for fields of frequency 50 per second were 



obtained, which shows the general effect. 



The results obtained are shown in Table II, and one set with direct 



fields, as well as the approximate values with the alternating fields, are shown 



as curves in fig. 2. 



Table II. 



Loads in grammes per sq. cm. 



Field H = 30 c.g.s. units per amp. 



From the values in Table II and the curves in fig. 2 it will be seen that the 

 behaviour of nickel wire in transverse magnetic fields is the reverse of that in 

 longitudinal magnetic fields — that is, there is at first a slight indication of a 

 decrease in the rigidity — and that the main effect of the application of 

 transverse fields, for the strongest fields that could be applied (960 units), is 

 to increase the rigidity. 



It is possible that for higher magnetic fields than the strongest here 

 applied the curves may come to a maximum, then decrease, and cross the 

 axis in the manner of those obtained with longitudinal fields. From the 



