1911-12.] Transverse Induction Changes in Demagnetised Iron. 293 
applied field be reversed or the direction of the demagnetising force be 
rotated so that its tangent changes sign. If both these changes be made 
simultaneously, the sign of this theoretical effect ought to remain unaltered. 
The experimental results confirmed the above deductions, notwith- 
standing the fact that the direction of the demagnetising force did not 
remain constant during the demagnetisation process. This variation, the 
result of the demagnetising effect of the ends of the hollow cylinder used, 
was so considerable that general conclusions only were published. The 
complete paper, as then written, was held over, and the present communica- 
tion now takes its place. Differences between the two will be made 
apparent as this paper proceeds. 
Objects of Investigation. 
I. To investigate the induction changes which occur at right angles to 
the magnetising field when the iron has been previously 
(а) demagnetised by decreasing reversals of a force having a transverse 
component ; 
(б) left residually magnetised by a method of partial demagnetisation 
by decreasing reversals of a force having a transverse component. 
II. To co-ordinate the experimental results with the theory of rotatable 
molecular magnets based upon as simple assumptions as possible. 
Experiments \a repeat those referred to in the paper mentioned above, 
the direction of the demagnetisation remaining more constant owing to 
both the magnetic circuits being completed in iron. The substitution of 
partial demagnetisation, Ih, for residual magnetisation produced in the 
usual way will be discussed under the heading “ iEolotropy ” at a later 
stage. 
Molecular Theory. 
Weber’s theory of magnetic induction assumes that the molecules of iron, 
or other magnetic materials which have never been magnetised, are magnets 
pointing at random and equally stable, on the whole, in all directions. To 
express this, Maxwell supposes a sphere to be described and a radius drawn 
from the centre parallel to the direction of each of the molecules in the 
mass. Varying this illustration, the magnetic axes of the molecules (or 
the resultant axes of stable molecular groups) may be regarded as diameters 
of a sphere with north and south polarity. It is supposed that any unit of 
area on the surface of this sphere contains an equal number of N. and S. 
poles, that the extremities of the molecules (diameters) are equally spaced on 
this surface and equally stable in all directions. 
