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Proceedings of the Royal Society of Edinburgh, [sess. 
On some Relations between Magnetism and Twist. Parts 
II., III. By Cargill G. Knott, D.Sc. Edin., F.R.S.E., 
Professor of Physics, Imperial University , Tolcyo, Japan. 
(Read June 1st, 1891.) 
(Abstract.) 
Part II. contains a continuation of former experiments on the 
twists produced in the magnetic metals when they are under the 
combined influence of circular and longitudinal magnetisations. 
It is established that a cobalt rod of rectangular section twists 
left-handedly when a current is passed along it in the direction of 
magnetisation. That is, cobalt behaves like nickel. Iron, on the 
other hand, twists right-handedly, until very high fields are 
employed. These results seem to have a close connection with the 
magnetic changes of length in these metals; for iron expands in 
moderate fields, while nickel and cobalt contract, the former always, 
and the latter till high fields are reached. 
In the case of nickel an evident maximum twist is obtained for 
intermediate values of field. The occurrence of this maximum 
finds a ready explanation in terms of the theory suggested. 
In all cases the amount of twist produced by reversing one of the 
magnetising forces depends on which one is reversed. Generally 
the twist is greater when the longitudinal field is reversed than 
when the current along the wire is reversed. For low fields in the 
case of iron and nickel it is, however, the current reversal that pro- 
duces the greatest twist. These various phenomena give very 
instructive illustrations of the magnetic after-effect or hysteresis. 
In Part I. an expression was given for the twist in terms of the 
elongations in a thin walled tube of given radius, under the com- 
bined influence of given circular and longitudinal magnetisations. 
From the observed maximum twists in iron and nickel wires now 
given, a comparison is made between the elongation coefficients 
which enter into the formula for the tubes of equal diameter. The 
comparison is in remarkable accordance with the direct comparison 
of elongations as furnished by Mr Bidwell’s measurements. 
Part III. contains a discussion of the magnetic consequences of 
