66 Prof. Tyndall on the Dynamical Theory of Heat. 



the "remarkable exception" of Prof. Tait. Had it caught my 

 eye, of course it would have been gathered up as the others, but 

 it would no more have affected my statement that the deter- 

 minations of 1843 varied from 1040 to 587 foot-pounds, than 

 the number 742 actually contained in my Table. 



But have 1 really omitted to give Mr. Joule due credit 

 for this experiment? Assuredly not. I was well acquainted 

 with it, though when collecting the results for my book I 

 overlooked it. In my morning lectures I referred to it thus : — 

 " He (Mr. Joule) also urged water through capillary tubes, and 

 determined the amount of heat generated by the friction of the 

 water against the sides of the tubes ; and the results of all his 

 experiments leave no shadow of doubt upon the mind, that, under 

 all circumstances, the quantity of heat generated by the same 

 amount of force is fixed and invariable." I have publicly 

 repeated this statement in print three times, to Prof. Tait's own 

 knowledge, since it was first uttered. 



And now I would ask my assailants, as men of honour, 

 whether they had this experiment in their minds when they 

 wrote the passage commented on ? If so, by what right do they 

 call this isolated result, stuck into the middle of a paragraph, 

 without data, and without a word to indicate the precautions 

 employed, " a well-planned and executed series of experiments V 

 Why, moreover, did they displace the number 770 by the exact 

 equivalent 772 ? When I think of the men who will read this 

 last paragraph of Prof. Tait and pass judgment on it, I am 

 restrained from making any further effort to disentangle it ; nor 

 shall I deem it necessary to answer any further remarks of this 

 kind. 



One word in conclusion. For reasons far too long to be here 

 stated, I regarded Prof. William Thomson as my real assailant 

 in ( Good Words/ and wishing to show my readiness to settle 

 our differences in an open manly way, I addressed him to the 

 exclusion of Prof. Tait. To cast a slight upon Prof. Tait was 

 not necessary to my defence; and as far as the first paragragh 

 of my letter to Prof. Thomson appears to convey such a slight, I 

 should wish it unwritten. For his sake, and not for mine, I 

 could wish the same with regard to the last paragraph of 

 Prof. Tait's last communication. 



Royal Institution, June 23, 1863. 



I had the happiness of receiving a few days ago a letter from 

 Dr. Mayer — the first which has ever passed between us — an 

 extract from which will interest many of the readers of the 

 Philosophical Magazine : — 



" Esteemed Sir, — I hardly know how to find words to express 



