208 
Proceedings of the Royal Society of Edinburgh. [Sess. 
XY. — On the Hall and the Transverse Thermomagnetic Effects 
and their Temperature Coefficients. By F. Unwin, M.Sc., 
Assistant Lecturer in Physics, Heriot-Watt College, Edinburgh. 
Communicated by Professor F. G. Baily. 
(MS. received May 5, 1914. Read June 15, 1914.) 
Introduction. 
Of the more recent researches on the subject of this paper, mention may 
be made of the work of H. Zahn * on the sralvanomavnetic and thermo- 
O 
magnetic effects in various metals. Zahn has measured these effects in 
many different metals, and has used his results to test the electron theory 
of the properties of metals as developed by P. Drude. He has also 
determined in some cases the temperature variation of the effects. 
The author of the present paper has confined his attention to the 
thermomagnetic transverse effects and the Hall effect. These have been 
measured in magnetic fields of various strengths and at temperatures 
varying over a range of about 100 Centigrade degrees. 
The experiments were carried out with a view to obtaining some light 
on the electron theory, and the ratios of the effects are discussed in relation 
to this theory. 
Definition of the Coefficients of the Effects and the 
Convention with respect to the Signs. 
In accordance with the custom of other workers, the Hall coefficient is 
denoted by R, the Thermomagnetic Temperature Effect by S, and the 
Thermomagnetic Potential Effect by Q. 
The directions of the effects corresponding to positive values of these 
coefficients are indicated by the diagrams (fig. 1) given below; it being 
understood that the magnetic field is in each case directed downwards 
at right angles to the plane of the diagram. 
The value of S is found as usual by calculating the transverse 
temperature difference in a plate 1 cm. broad placed in unit magnetic field, 
when the temperature gradient along the axis is 1° C. per cm. 
The value of Q is found by calculating the transverse E.M.F. (in 
electromagnetic units) under the same conditions. 
* Ann. d. Phys., xiv. p. 886, 1904. 
