232 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



mum H is the same for all three. In each case the iron was carried 

 around its hysteresis cycle a large number of times. No demagnetiza- 

 tion was attempted ; the change from one curve to another consisted 

 merely in the change of the number of steps. 



The maximum value of B was approximately 6000. The vertical 

 ordinate is in terms of throws of the galvanometer. If one half the 

 throw for a complete reversal of the maximum H be taken as 833, 



the maximum values of B for the 

 three curves would be represented 

 by 824, 770, and 692; that is, for 

 the introduction of four steps in- 

 stead of one into the hysteresis 

 curve, the maximum value of B 

 has fallen 1 per cent, for 28 steps 

 7.6 per cent, and for 56 steps 17.4 

 per cent. 



For massive iron therefore it is 

 undoubtedly true that a change in 

 the number of steps of magnetization 

 has a certain measurable effect on 

 the final magnetic condition of the 

 iron. 



In such masses of iron the eddy 

 currents can in no wise be neglected. 

 There is nothing to show that the 

 phenomena may not be accounted 

 for by their action as well as by 

 some inherent property of the iron 

 itself; or indeed by both of these causes existing side by side. For 

 more definite conclusions it is necessary to eliminate one of the fac- 

 tors. The former yields the more readily. 



It has been shown that in the case of a long cylinder the reduction 

 of the eddy currents^ can be carried to any desired point by a sufficient 

 lamination of the iron, and a toroid, if the radius of the ring be large 

 enough in proportion to that of the solid mass, presents a form approx- 

 imating that of a cylinder. While a mathematical demonstration will 

 not be attempted, I think it safe to regard lamination as playing in 

 my toroid the same role as in a cylinder, and by the elimination of 

 eddy currents offering a means for deciding to what we are to attribute 

 the effect of variation in the methods of magnetization. 



Figure 2. 



These Proceedings, 43, 161-182 (1907). 



