260 PROCEEDINGS OF THE AMERICAN ACADEMY. 



for all three cases. What variation there was seems to have had no 

 effect. 



An 8-step reversal with a maximum B of 3100 was tried and com- 

 pared with a 1-step reversal of the same field. The ratio of the former 

 to the latter was as 914 to 922. By the use of a 10-step reversal and 

 a maximum B of 8000, it was found that the 1-step reversal corre- 

 sponding yielded a maximum B about 2 per cent smaller. Such an 

 unexpected phenomenon led to the testing of the core, excited by 

 a strong field, by means of iron filings spread on a sheet of paper 

 directly above it. A slight consequent pole appeared at one spot. 

 Lack of knowledge of the other factors entering into the work pre- 

 vented any attempt to determine whether or not such a pole would 

 affect the building up of the magnetic field. The core was immediately 

 discarded. 



In so far as they were consistent the results obtained from this core 

 show that the number of steps taken in going from one magnetic con- 

 dition to another is immaterial, provided the flux change be always in 

 the same direction. The inconsistent results support my view that 

 when a process of demagnetization intervenes between two processes of 

 magnetization one is not at liberty to regard the first eight or ten 

 hysteresis cycles that may be passed over in the first magnetization as 

 necessarily equal to the corresponding hysteresis cycles of the succeed- 

 ing magnetization. In fact, I should hesitate to compare any two sets 

 of readings if I had demagnetized the specimen between the two. 



If one were to take the trouble to go through exactly the same 

 process in each demagnetization, that is, use exactly the same number 

 of steps, reverse the field the same number of times, and see to it that 

 the field maxima were always the same in both order and magnitude 

 for the corresponding steps, it is presumable that in time one could get 

 the iron into such a condition that consistent reversal-flux curves similar 

 to those given for core I would be obtained. Then one would 

 be justified in comparing the flux change produced by any given 

 reversal with the corresponding flux change produced after the next 

 demagnetization. Such a procedure would be extremely laborious. 

 However, it is not inconceivable that certain parts of the demagnet- 

 ization have a greater effect than others on the final non-magnetic 

 condition and that attention to those alone would be sufficient to 

 assure consistent results. There is an opportunity here for further 

 research. 



