276 Electromotive Forces in Voltaic and Thermoelectric Piles. 



temperature if the beat tends to oxidize one metal more than 

 another, or in any other way to interpose a barrier between 

 metal and active medium ; but the fact has no thermoelectric 

 interest whatever. 



c. The total E.M.F. of a thermoelectric circuit is the sum 

 of the forces in the different parts of that circuit, viz. at the 

 junction and in the metals, and has nothing on earth to do 

 with Volta's, or Crookes's, or Hall's, or anybody else's 

 " effect" except Peltier's and Thomson's. 



d, e. The Peltier-effect at a junction is a measure and conse- 

 quence of the E.M.F. located there. 



/, g. Heat (or more generally energy) is generated or 

 destroyed at places where the current does work or has work 

 done upon it, i. e. whenever it is opposed or assisted by an 

 E.M.F., and nowhere else. 



In conclusion, a word of explanation. In the effort to be 

 clear, and to bring opposing views into sharp collision and 

 contrast, I fear I have been dogmatic, and sometimes perhaps 

 in appearance arrogant. I beg to assure all who may do me 

 the honour to read this lucubration that it is only an appear- 

 ance. I doubt not but that much can be said on the other 

 side, but I have also no doubt that whatever can be said icill 

 be said ; and it is essentially because of the energy and ability 

 of my opponents that I am forced to strike out vigorously. 



Professors Ayrton and Perry very naturally endeavour to 

 crush me with the weight of the name of Sir William Thomson, 

 and were I to listen to an argument ad verecundiam I should 

 indeed hold my peace. But in science one need not be silenced 

 by authority, and I may well be pardoned for stating strongly 

 the views which commend themselves to me. Sir William 

 himself would be the first — as a matter of fact has been the 

 first — to wish it. If Sir William Thomson really agrees in 

 the main with the doctrines expounded by Ayrton and Perry, 

 as I have some reason to believe he does, it is no part of 

 my business to explain the phenomenon : if it were, I might 

 tentatively suggest that perhaps he has not very recently, or 

 very carefully, considered the subject. Nor can I say that 

 I should wish him to trouble himself to do so. Let him 

 reserve his tremendous powers and energies for higher and 

 more momentous problems, such as the nature of Matter, of 

 Elasticity, and of Light. The seat of E.M.F. in a pile, 

 whether it be voltaic or thermal, is comparatively a small affair, 

 and can if necessary be settled without his active participation 

 in the controversy. 



University College, Liverpool, 

 February 13, 1886. 



