378 Prof. TyndalFs Remarks on the 



But the responsibility is yours. No taint of personality is to be 

 found in anything that I have ever written regarding you; even 

 when facts were against you I held my peace. When I wrote 

 my brief and temperate remonstrance to the Philosophical 

 Magazine,- all that I have stated in this letter was known to 

 me. I then knew, as well as I do now, that your treatment 

 of Mayer could not bear the light of criticism ; still my remon- 

 strance breathed no syllable of accusation. My desire was to 

 clear myself, and not to criminate you, trusting that the trans- 

 lations of Mayer's works now appearing in the Philosophical 

 Magazine would in due time set public opinion right regarding 

 him. I hoped that good sense and gentlemanly feeling would 

 so far predominate as to induce you to withdraw an accusation 

 which, though vaguely uttered, was offensive. Had you done 

 so, this discussion would have perished in the bud, and I should 

 never have written a sentence which could be personally dis- 

 agreeable to you. But instead of withdrawing your accusation, 

 you repeat it, and thus compel me in self-defence to lay a true 

 statement of the case before the scientific public, and invoke its 

 judgment between us. 



I have the honour to be, Sir, 



Your obedient Servant, 



John Tyndall. 



I have studied Mayer's first memoir attentively, and am 

 unable to affix a definite meaning to the statement of Prof. 

 Thomson that it was "by a lucky chance he got a true result 

 from an utterly false analogy." The object of Mayer's paper, 

 as he himself informs us, is to give to our ideas of "force" the 

 same precision as to our ideas of " matter." He finds in the 

 universe two systems of causes, from the one to the other of which 

 there is no transition ; the members of the one system possess the 

 attributes of ponderability and impenetrability, those of the other 

 system do not ; the one consists of the different kinds of mat- 

 ter, the other of the different manifestations of force. The first 

 quality of all causes he affirms to be indestructibility (Unzerstor- 

 lichkeit). A force cannot become nothing; and just as little can 

 a force be produced from nothing. Forces, he affirms, are inde- 

 structible and convertible, different forms of one and the same 

 object. When a force has wrought an effect equal to itself, it 

 ceases by that act to have an existence. A weight resting upon 

 the earth is not a force ; it is incapable of producing motion, 

 incompetent, for example, to lift another weight. A raised 

 weight is a force (potential energy) ; a falling weight which 

 possesses motion (dynamic energy) is a force. The first force, 

 which consisted simply in the separation of the weight from the 



