E. A. Rowland^ Studies on Magnetic Distribution. 



Now we have found (equa 

 and this in Green's formula (equation 14) giv 



(16) 



I identical with my own when }a is large, as it always is 

 ise of iron, nickel, or cobalt at ordinary temperatures. 

 I X is measured from the center of the bar, my equation 



2 + £-2 



(IV) 



The constant part of Biot's formula is not the same as this ; 

 but for any given case it will give the same distribution. 



Both Biot and Grreen have compared their formulae with 

 Coulomb's experiments, and found them to represent the dis- 

 tribution quite well. Hence it will not be necessary to consider 

 the case of steel magnets very extensively, though I will give 

 a few results for these farther on. 



At present let us take the case of electro-magnets. 



For observing the effect of the permeability, I took two wires 

 12-8 inches long and 19 inch in diameter, one being of ordi- 

 nary iron and the other of Stub's steel of the same temper as 

 when purchased. These were wound uniformly irora end to 

 end with one layer of quite fine wire, making 600 turns in that 

 distance. 



In finding A from Q''^, the latter was divided by 47rAL, ex- 

 cept at the end, where the end section was included with aL 

 in the proper manner, x was measured from the end of the 

 bar in inches. 



