316 YOSHIJIKO KATO; 



Concluding Remarks. 



Since the nature of magnetism is not well known, I cannot 

 give any rigorous reasoning leading to the above equation. But 

 meanwhile let us try to explain it by the molecular theory. According 

 to this theory, the molecules of iron which find themselves on the 

 outer surface of the wire, are less constrained by the mutual action of 

 the molecules than those situated in the interior, and hence are more 

 ready to submit to the action of any disturbing cause. Therefore, if 

 a given magnetic force is applied to the wire these surface molecules 

 are first affected. Then the molecules lying next the outermost have 

 their stability reduced, and will be the next to submit, and so on. 

 Thus, the process of magnetisation diffuses itself gradually from the 

 outermost layer into the interior of the mass. Hence, from analogy 

 with Fourier's solution of the propagation of heat, we may put, in a 

 cylindrical conductor, 



3 = a - |>» e n • 



Now, since we cannot of course use an infinite number of terms in 

 the actual calculation, we must cut down the expression and reduce 

 it to a small finite number of terms. But this cutting out terms can 

 not be done without somewhat affecting the values of c and k in some 

 at least of the surviving terms. For, although as regards those terms 

 which we are going to neglect, the values of the c's are small, yet the 

 values of the k's are also small, and the terms cannot, therefore, be ne- 

 glected in the ordinary way. But, as long as t is not large, we can 

 approximately substitute the sum of all these terms by a single term. 

 For, let these terms be — 



T = c 4 c -A V + c 6 ß-V + c 6 e~V+ 



