DYNAMICAL THEORY OF HEAT. 143 



other friends, have also given much valuable assistance during a great part of 

 this time, in the different experimental investigations, of which the results are 

 now laid before the Royal Society. 



126. " Only nugatory results were obtained until recently, from multiplied and 

 varied experiments both on copper and iron conductors ; but the theoretical anti- 

 cipation was of such a nature, that no want of experimental evidence could in- 

 fluence my conviction of its truth. About four months ago, by means of a new 

 form of apparatus, I ascertained that resinous electricity carries heat with it in an 

 unequally heated iron conductor. A similar equally sensitive arrangement showed 

 no result for copper. The second hypothesis might then have been expected to 

 hold ; but to ascertain the truth with certainty, I have continued ever since get- 

 ting an experiment on copper nearly every week, with more and more sensitive 

 arrangements ; and at last, in two experiments, I have made out with certainty, 

 that vitreous electricity carries heat with it in an unequally heated copper con- 

 ductor. 



" The third hypothesis is thus established ; a most unexpected conclusion, I 

 am willing to confess. 



" I intend to continue the research ; and hope not only to ascertain the nature 

 of the thermal effects in other metals, but to determine its amount in absolute 

 measure in the most important cases, and to find how it varies, if at all, with the 

 temperature ; that is, to determine the character (positive or negative) and the 

 value of the specific heat, (varying or not with the temperature,) of the unit of cur- 

 rent electricity in various metals. 1 ' 



127. The relations 



'•-'•=f-*r • • ■ (16) and ¥ = } fJr m <"> 



established above, " show how important it is towards the special object of 

 determining the specific heats of electricity in metals, to investigate the law of 

 electro-motive force in various cases, and to determine the thermal effect of elec- 

 tricity in passing from one metal to another at various temperatures. Both of 

 these objects of research are therefore included in the general investigation of the 

 subject. 



128. " The only progress I have as yet made in the last-mentioned branch of the 

 inquiry, has been to demonstrate experimentally, that there is a cooling or heating 

 effect produced by a current between copper and iron, at an ordinary atmospheric 

 temperature, according as it passes from copper to iron, or from iron to copper, 

 in verification of a theoretical conclusion mentioned above ; but I intend shortly 

 to extend the verification of theory to a demonstration, that reverse effects take 

 place between those metals, at any temperature above their neutral point of about 

 280° Cent. ; and I hope also to be able to make determinations in absolute 



VOL. XXI. PART I. 2 Q 



