252 M. Werner Siemens on the 
s not directly applicable on account of the magnetism of the 
end-surfaces. : 
The distribution of magnetism in a bar of definite length is 
quite different if the magnetizing force acts equally on all parts 
of the bar. The decrease in magnetic moment from the 
middle of the bar towards the ends loses then its logarithmic 
character, and assumes the form of a catenary (as already 
shown by Rees), or nearly that of a parabola. In a rod 150 
millim. long and 7:70 millim. diameter, which was enclosed 
in a glass tube of double length uniformly wrapped with a 
magnetizing-coil, the magnetic moment of each section could 
be determined by means of an induction-coil wound over the 
middle of the tube, when the direction of the magnetizing- 
current was reversed. 
In the following Table the magnetic moments are given for 
the same rod at distances of from 20 to 70 millim. from the 
centre when the bar was uniformly magnetized, and when 
magnetized at the centre. The current-strengths were so 
chosen that the magnetism at the end of the rod was nearly 
the same in both cases. 
Distance x of the 
secondary coil 
from the centre of 
Deflection when | Deflection when 
magnetized uni- | magnetized at the 
ana formly. middle. 
millim millim. millim 
2 287 463 
30 263 378 
40 233 302 
50 195 229 
60 145 160 
70 87 92 
Calculating from the equation to the parabola 
22 
Yy a 2p, 
the deflections of the second column for uniform magnetization 
give for 2p the values 23, 22, 22, 23, 23, 22. Calculating 
from the numbers of the third column by means of the for- 
mula 
2 
loo a3 
oy ae 
the quotients 7 for a constant displacement of the induction- 
1 
