1884.] The Tliomson Effect and Properties of Metals. 25 



cumstance was also observed, viz., that the cathode which most 

 readily received a deposit was frequently the one composed of the 

 same kind of metal as that which was being deposited. I am now 

 examining these new facts. 



May 8, 1884. 

 THE PRESIDENT in the Chair. 



The Presents received were laid on the table, and thanks ordered 

 for them. 



The following Papers were read : 



I. " On a Relation between the Coefficient of the Thomson 

 Effect and certain other Physical Properties of Metals." 

 By SHELFORD BIDWELL, M.A., LL.B. Communicated by 

 Prof. FREDERICK GUTHRIE, F.R.S. Received April 23, 

 1884. 



The magnitude and direction of the Thomson effect depend upon 

 a coefficient which is always the same for the same metal, but varies 

 with different metals. Professor Everett, in his " Units and Physical 

 Constants," p. 151, gives a table based upon Tait's thermoelectric 

 diagram ("Trans. R.S.E.," vol. xxvii, p. 125), in which the thermo- 

 electric values of a number of metals, referred to lead as zero, are 

 given in the form +{lt, where ft is a number which for a given 

 metal- is proportional to the tangent of the inclination of the line 

 representing the metal in Tait's diagram, and therefore to the co- 

 efficient of the Thomson effect. 



Since all the physical properties of a metal are to some extent 

 affected by heat, it seemed probable that a connexion might be found 

 to exist between certain of these properties and the Thomson effect. 

 A short examination showed that, as a rule, the coefficient of the 

 Thomson effect is positive in those metals which have a great specific 

 electrical resistance and specific heat, and negative in those which 

 are distinguished by a great coefficient of expansion. I therefore 

 made several attempts to ascertain whether the Thomson coefficient 

 might not be some definite function of the specific resistance, specific 

 heat, and coefficient of expansion ; and though I have not been per- 

 fectly successful, it appears from the subjoined table that there is a 

 close relation between them. 



