Relation between Heat and Mechanical F<mei'. 205 



may be. Indeed both substances bear so much the stamp of 

 simplicity, they exhibit so decided a chemical antagonism 

 towards each other, both of them, conjointly with their remark- 

 able product "water," act throughout the domain of our science 

 so extensive and important a part, that we can hardly help 

 suspecting them to be active in some way or other in most, if 

 not in all chemical reactions,and seeing in oxygen and hydrogen 

 the hinges upon which the whole chemical world turns. The 

 theory of Davy, seducing and plausible as it appears at first 

 sight, has possibly proved a check, rather than a spur, to the 

 development of chemistry, on account of its having changed, 

 perhaps, the true point of view from which oxygen ought to 

 be looked at. For if oxygen should happen to act that all-^ 

 important part which Lavoisier and the chemists of the last 

 century assigned to that element, it is not difficult to see that 

 the views of Davy are calculated to retard the progress ofj 

 theoretical chemistry rather than to accelerate it. 



I need not say, that the considerations I have taken the 

 liberty to submit to you have been entered into with the view 

 only of drawing the attention of philosophers towards a subry. 

 ject which seems to me to be of considerable theoretic^aliinohr. 

 portance, and worthy of our study. ^■>3f'^,^a9-'i{j 



jon bflB tbiofi oitmium hssino^yxo ; C. F. Schcenbein* orj 



X^XI. On the Existence of an Equivalent Relation between 

 ^"'Heat and the ordinary Forms of Mechanical Power, By 

 '^^ITames p. Joule, Esq. ., 



To the Editors of the Philosophical Magazine and JournaU ^ 



Gentlemen, 



nPHE principal part of this letter was brought under the 

 ■*• notice of the British Association at its last meeting at 

 Cambridge. I have hitherto hesitated to give it further pub- 

 lication, not because 1 was in any degree doubtful of the con- 

 clusions at which I had arrived, but because I intended to 

 make a slight alteration in the apparatus calculated to give 

 still greater precision to the experiments. Being unable, how- 

 ever, just at present to spare the time necessary to fulfil this 

 design, and being at the same time most anxious to convince 

 the scientific world of the truth of the positions I have main- 

 tained, I hope you will do me the favour of publishing this 

 letter in your excellent Magazine. 



The apparatus exhibited before the Association consisted 

 of a brass paddle-wheel working horizontally in a can of water. 

 Motion could be communicated to this paddle by means of 



