SHUDDEMAGEN. — DEMAGNETIZING FACTORS TOR IRON RODS. 241 



ellipsoid in order to form the corresponding cylinder, the surface mag- 

 netism o- is shifted nearer to the ends of the rod and should exert less 

 demagnetizing force. To be sure, we now have some volume magne- 

 tism, p = — Divergence 7, in the cylinder, which does not exist in the 

 ellipsoid, but the effect of this 

 is probably always extremely 

 small. On the whole we feel - 040 . 

 certain that Mann's value is jj 

 quite near the truth, and is 

 probably even a trifle too 036 

 large. 



Table XV, on page 239, 

 gives briefly all the results .030 

 obtained on demagnetizing 

 factors for the region in which 

 they are practically constant, 025 

 that is, for the iron cylin- 

 ders up to about I — 800, or 

 B = 10,000. 



The values of N as obtained 02 ° 

 for the various diameters of 

 rods in the present investi- 

 gation are given in Tables .015 

 XVI and XVII on the pre- 

 ceding page. They were ta- 

 ken from the tables given for 010 

 each separate rod, and are 

 fairly constant over the range 

 from B = 3000 to B = 9000. 



.005 



40 



50 



M 



"80 



100 



150 



JO 



Figure 20. 



15 



20 



The values of N of these 

 tables have been plotted in 

 Figure 20 against the corre- 

 sponding diameters of the 

 rods. The points connected 

 by straight lines are the re- 

 versal method values, while 

 those left unconnected are 

 the ones taken by the prin- 

 ciple of steps. It seems to be shown that the values of N experience 

 a rapid drop from D = 0.238 to about D = 0.50, and then remain 

 nearly constant as the diameter is further increased. 



For practical use in finding permeabilities Table XVIII has been 



VOL. XLIII. — 16 



Curves showing the variation in A T for 

 different diameters of iron rods. The num- 

 bers near curves give the corresponding 

 values of m. 



