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PROCEEDINGS OF THE AMERICAN ACADEMY. 



decreasing, and that the magnetization is becoming gradually more 

 and more uniform. At about 5 = 17,000 the curves rise the fastest, 

 showing that the middle portions of the rod are very nearly saturated 

 and take up more magnetization only very slowly, while for the coils 

 nearer the end the magnetization is still rapidly increasing. Figure 

 25, for the short rod (in = 25), shows that after B is about 20,000 

 under the middle coil, the curves all have points of inflection and now 

 approach the ordinate 100 per cent asymptotically. If we now con- 

 sider Figure 23, for the very long rod (in = 240), we see that here we 

 have a case of the magnetization being always very much nearer uni- 

 formity, so that the curves for coils 6, 7, and 8 are already in the 

 asymptotic stage for B = 15,000 under the coil 5, and the points of 

 inflection are near B = 10,000. When B = 15,000, the curve for the 

 coil 9, nearest the end of the rod, shows a tremendous upward shoot 

 from a long horizontal course near the ordinate 50 per cent. Since the 

 figure only gives the observations in the range of percentages from 80 

 to 100, it might be well to give the missing values here : 



In the case of the long rod the lowest fields used were still too high to 

 show a rise in the curves, corresponding to increased uniformity of 

 magnetization, as is seen in the other two figures. 



The results show that near the middle of a rod the induction is 

 practically the same for quite a little range, especially if the rod is fairly 

 long. Thus the curve 6 in Figure 23 shows that in the rod of length 

 about 458 cms. and m — 240, the induction for a distance 50 cms. 

 from the middle of the rod is always within about 2 per cent of the 

 induction at the middle portion. And curve B in Figure 24 proves 

 the induction at 14 cms. from the middle of the rod of length about 



