222 
Proceedings of the Royal Society of Edinburgh. [Sess. 
metals as copper, zinc, and aluminium, is of considerable theoretical 
interest. In accordance with the theory of the differential field, the sign 
of this effect should change along with the sign of the Hall effect, whereas 
in accordance with Drude’s statement of the theory it should be of the 
same sign in all metals. Zahn has measured the effect in several metals, 
but it so happens that, owing to the metals used, no definite conclusions 
can be drawn from the results. The author hopes to carry out further 
experiments on this point. 
( Issued separately August 4, 1914.) 
