9 2 CONFUSION OF TERMS. 



antiquity, but was also much better fitted. In saying 

 that Joule's missing this opportunity was remark- 

 able, it is not intended to imply that it was in any 

 way discreditable to his scientific insight. Joule was, at 

 that time, head and shoulders before any of his contem- 

 poraries in his appreciation of matters relating to the 

 connection between work and heat ; and it was not till 

 three years afterwards that Sir William Thomson, then 

 commencing his intimate friendship with Joule, recognizing 

 the incontestable evidence afforded by Joule's experiments, 

 and anxious, beyond measure, to reconcile the apparent 

 disagreement in the two principles, Joule's and Carnot's, 

 was yet for three more years baffled by their apparent 

 inconsistency, which arose from what was really a confusion 

 of terms. It was then Sir William applied Young's term 

 * Energy' to include everything resulting from or convertible 

 into the half of vis viva. Joule had used the term ' force ' 

 in the same sense as 'energy,' and continues to use it sub- 

 sequently, quoting in defence Leibnitz's definition : ' The 

 force of a moving body is proportional to the square of its 

 velocity, or to the height to which it would rise against 

 gravity.' 



The first paragraph quoted from Joule's paper of June, 

 1844, is of great interest as showing his early appreciation 

 of the bearing of his discoveries on the then very indefinite 

 u dynamical theories " of " heat " and of "gases" and as con- 

 taining an account of his own highly philosophical and 

 successful attempt to add definition to the previous ideas of 

 the motions of the matter constituting gases expressed 

 by succeeding philosophers, which ideas had taken intelli- 

 gible but still indefinite shape in Davy's hypothesis. 



But from a biographical point of view the paragraph 



