642 PROCEEDINGS OF THE AMERICAN ACADEMY. 



able influence on the value of c. This seems to me a new proof that 

 the Hall phenomenon is due to a deformation of the plate under the 

 influence of the magnetic field, and it is enough to explain the differ- 

 ences, often very great, observed between the values of c, for the same 

 body, by diff"erent experimenters." 



It is difficult to see how anyone who has tried the Hall eff'ect with a 

 variety of conditions as to the manner of supporting the metal under 

 examination can attribute this effect to any ordinary distortion of the 

 material. If distortion, or deformation, is the cause of the phenomenon 

 in question, this distortion must be something as remote from ordinary 

 bending and twisting as are the changes of molecular orientation which 

 we imagine to accompany or constitute magnetization. 



We might, therefore, pay little attention to the suggestion of ]\Ioreau, 

 if he had not given and supported with some experimental evidence an 

 exceedingly simple formula, 



eTe ^ P = hTe -^ S, (5) 



in which eT^e = the Hall coefficient, 



},Te= " Nernst " 

 p = " specific electrical resistance, 

 s = " mechanical equivalent of the Thomson-effect 

 coefficient, that is, the amount of heat energy (ergs) absorbed by the 

 unit current (absolute) of electricity per second in going, according to 

 the ordinary convention of current direction, through the metal from a 

 point where the temperature is T degrees C. to a point where it is 

 (r+i) degrees C. - 



This formula of Moreau, if it could be substantiated by further 

 experimental evidence, would prove disturbing to the point of view 

 from which the present definition of the Hall coefficient was framed, 

 even if it did not lead to the conclusion that the Hall efTect and its 

 various allied effects are due to a deformation of some kind in the 

 material showing these phenomena. For it is to be noted that in the 

 definition of ^Te the relation of the transverse potential-gradient to 

 longitudinal current-strength, not to the longitudinal potential-gradient, 

 is expressed. The reasons for this are two: 1st, a notion held by the 

 discoverer at the time of the discovery that the new effect was due to 

 the action of magnetic force on a current of electricity, as such, not to 

 the action of such force on a medium containing lines of electrical force,^ 



^ At the suggestion of Professor Rowland an attempt was made to rotate 

 by magnetic force the equipotential Hnes of a piece of glass under electrical 

 stress. The result was negative. — E. H. H. 



