265 



of temperature, then it is plain the deflection produced by such 

 contact will be reversed by attrition of the metals while at 

 such unequal temperatures. 



IX. If the deflections be all on the same side of the mag- 

 netic meridian, which are produced, 1st, by the contact of the 

 two metals at unequal temperatures ; 2nd, by the attrition of 

 the metals when they are at equal temperatures ; and 3rd, by 

 their attrition when they are at unequal temperatures : then 

 there can be no reversal. 



X. Whether the deflection of the needle will take place 

 on the eastern or western side of the magnetic meridian will 

 be determined by the nature of the metals engaged; by the 

 relative temperatures at which contact or attrition has been 

 effected ; and by the peculiar influence of the metal that is 

 placed in connexion with, and is active at each extremity of 

 the coil of the galvanometer. 



XI. The condition necessary to the production of deflec- 

 tion by contact of two different metals is, that heat shall be 

 at that moment entering or leaving one of them, or that heat 

 shall be unequally entering or unequally leaving both of them; 

 no matter whether the inequality depend on difference of sup- 

 ply, of conduction, of capacity, or on unequal diffusion of 

 heat arising from difference of mass of the metals, or on more 

 than one or all of these causes conjointly. The deflection 

 caused by the unequal entrance of heat into metals in contact 

 will be on the side of the magnetic meridian opposite to that 

 on which it would be, if heat were leaving them unequally. 



XII. If a metal of a certain class be heated in one part, 

 while the remainder of it is maintained at a much lower tem- 

 perature ; and if the hot part be brought in contact with a 

 metal of a different class, which is at a much lower tempera- 

 ture throughout its mass, the deflection produced will be on 

 the side of the magnetic meridian opposite to that on which it 

 would have been if the first-mentioned metal had been equally 

 heated in all parts. And it is possible to heat such portion 



