1904 - 5 .] Magnetic Quality in Molecular Assemblages. 1043 
rounded edges and corners, and it is everywhere concave to its 
centre. 
If a, /3, y be the direction cosines of the radius, r, drawn from 
the origin to a point on the surface, the direction cosines of the 
outwardly drawn normal at that point are a 3 / Ja 6 + /3 6 + y 6 , etc. ; 
and the direction cosines of the line drawn perpendicular to the 
radius vector, in the plane containing it and the normal, so that 
the angle between it and the outward normal is obtuse, are 
a(Q - a 2 )/ Ja 6 + /3 6 + y 6 - Q 2 , etc. Also, if p be the length of 
the perpendicular drawn from the origin to the tangent plane 
at the extremity of r, we have a 6 + /3 6 + y 6 = 1 /ph s , and Q = 1 /r 4 . 
Thus the magnitude of the transverse force is B^/r 2 -p 2 /2pr 4: . 
Now - B/2r 4 is the variable part of the internal force in the 
direction of magnetisation. Therefore, if the inwardly drawn 
radius vector be taken to represent this component, the subnormal 
will represent the transverse component. So that, on this scale, 
the intercept of the inwardly drawn normal by the central plane 
drawn perpendicular to r represents the total variable part of the 
internal force. 
16. Magnetisation in Principal Planes. — Experimental facts to 
