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LVIIL Note on Professor TyndalFs " Remarks on the 

 Dynamical Theory of Heat." 



To the Editors of the Philosophical Magazine and Journal. 



Glasgow College, 

 GENTLEMEN, May 4, 1863. 



THE Philosophical Magazine just published contains a letter 

 addressed to me, and bearing Dr. TyndalPs signature. As 

 I never received the original, I am surprised to see this use made 

 of my name. 



Allow me to say that I consider it a great injury to myself 

 that I should be made even apparently the medium of the state- 

 ments which Dr. Tyndall addresses to me regarding my friend 

 Professor Tait, whose distinguished position in science, as one of 

 the first mathematicians of our time, as an author, and as an 

 experimenter, should have preserved him from such liberties. 



The tone adopted by Dr. Tyndall in addressing myself is of a 

 character, I believe, unprecedented in scientific discussion. It is 

 such that I decline to take part personally in any controversy 

 with him, or to notice his letter further than to say that on all 

 the scientific questions touched upon in it I am ready to support 

 the correctness of the opinions, and information, in the article in 

 ' Good Words ' by Professor Tait and myself, and that I shall 

 do so when I see proper occasion. 



I remain, Gentlemen, 



Your obedient Servant, 



William Thomson. 



LIX. On the Conservation of Energy. By P. G. Tait, M.A., 

 Professor of Natural Philosophy in the University of Edinburgh. 



My dear Sir David Brewster, 



I FEAR I must trouble you with a second letter on the history 

 of the "Conservation of Energy;" but it shall be as brief 

 as possible. And, as Professor Tyndall has demanded, though 

 not from me, proofs of some assertions made in my former letter, 

 I shall take this opportunity of giving them. 



The conservation of energy as regards ordinary mechanics was 

 completely stated by Newton, in its differential form, as a corol- 

 lary to his third law of motion, in the remarkable words, " Si 

 {estimetur agentis actio ex ejus vi et velocitate conjunctim, et simi- 

 liter resistentis reactio (estimetur conjunctim ex ejus partium sin- 

 gularum velocitatibus et viribus resistendi ab earum attritione, co- 

 hasione, pondere, et acceleration oriundis ; erunt actio et reactio 

 sibi invicem semper cequales." In an integral form it 



Phil. Mag. S. 4. Vol. 25. No 170. June 1863. 2 G 



