244 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



It is, therefore, out of the question to expect any consistency in results 

 obtained by comparing reversals if a process of demagnetization inter- 

 venes. If 1-step reversals on two successive curves are not comparable 

 and, so far as can be seen, follow no exact law, it is not logical to obtain 

 a hysteresis curve of a given number of steps, demagnetize the iron, 

 obtain a second curve of a different number of steps, and, because the 



maximum B of one curve 

 is greater than that of 

 another, declare that the 

 number of steps affects the 

 magnetic condition of the 

 iron. 



This variation in mag- 

 netic condition is due, I 

 suppose, to the past history 

 which theoretically can 

 never be twice exactly the 

 same. It may depend on 

 the previous magnetiza- 

 tions or demagnetizations 

 or on both. No complete 

 distinction between the 

 effect of the two is possi- 

 ble, but some few things 

 appear to be true. The 

 remarkable drop in the first 

 curve and rise in the second 

 followed by the more rapid 

 rise in the later curves seem 

 to show the result of pre- 

 vious magnetic history, in 

 particular, the previous 

 magnetizations. For as the number of magnetizations increases, the 

 curves assume more and more the same general form. The variations 

 in the number of reversals required for any particular magnetization 

 to reach a constant state, even after the form of the curve remains 

 unchanged, leads one to suspect that the demagnetization plays an 

 important part. If the iron be treated on each occasion with the 

 same magnetic field, the process of demagnetization is practically the 

 only variable. In it the number of reversals for any given magnetic 

 field and sometimes the number of steps used varied considerably. 

 There is no reason for supposing that a change in the demagnetizing 



Figure 6. Set II: B6000: fifth magnetiza- 

 tion; O indicates 1-step reversals; X 3-step 

 reversals. 



