EFFECT OF STRESS ON MAGXETIZATIOX. 7 



adjusted, that tlie rovorsal of the inaguetizing field, if it was 

 repeated two or three times, caused an qv[ua\ deflection of tlic 

 galvanometer. Tiiis method was found to be very sensitive, a very 

 small change of the current in the compensating system produc- 

 ing a decided inequality of the galvanometer deflections in oppo- 

 site directions. 



Tiie tension effect was first tried. To wipe out any uncertain 

 remanent stress of the specimen, cycles of tensions, from zero to 

 the greatest to be used for the specimen, were passed through 

 before commencing any experiment. As a preliminary to test the 

 working of the arrangement, a series of increasing fields was 

 applied step by step under a constant tension, and the increase 

 of magnetization was observed by the galvanometer. After a 

 complete demagnetization, a weak field was applied and kept con- 

 stant. While the observer was watching the galvanometer, the 

 experimenter applied a series of increasing tensions step by step ; 

 the throw of the galvanometer at each step was recorded. Then 

 the tension was decreased step by step, and the corresponding 

 deflection were sometimes noted. After passing through several 

 cycles of the tensions, the observation was rejieated. After a 

 complete demagnetization, the procedure was repeated for another 

 higher field and so on. The number of fields chosen was natu- 

 rally large for the region where the change of magnetization was 

 considerable, but rare where it was small. The magnetizing cur- 

 rent wiS found to remain nearly constant during an experiment, 

 except in strong fields, where it was sometimes found to vary 2 

 or 3 per cent. The reading of the ammeter was always observed 

 both before and after the experiment, and the mean was taken. 



Instead of increasing the tension step by step, the maximum 

 tension was often applied at once ; but it was found that the 



