88 Prof. J. J. Thomson and Mr H. F. Newall, [Feb. 28, 
of the crevasse; that these poles are situated at some distance 
from the core ends, even from the roughly worked ends, when these 
are set touching one another; that the distance of the poles from 
AGN 
Fic. 2. WoRKED ENDS SEPARATED BY ONE DIAMETER. 
the ends of the cores changes with the separation of the worked 
ends; and that there is a neutral point (marked * in the figures) 
whose locus is a circle round the core in a plane perpendicular to 
the axis, and the centre on the axis in the middle of the crevasse. 
Assuming that the external action of the cores may be taken as 
due to a distribution of magnetism representible by poles placed at 
a definite position in the cores, we may express the distance of the 
neutral point from the axis in terms of the distances between these 
poles. Consider the cut cores as replaced by four poles as in 
the figure 3. 
Qu 
Fic. 3. 
Let the separation of the middle poles be 2a, and the distance 
between one middle pole and the nearest outer pole be 1. Then x 
the distance of the neutral point from the axis is related to a and 
l by the equation 
=x (a+ Lite! (a+ 1)3, 
