Intelligence and Miscellaneous Articles, W| 



after mine can only affect me by offering additional evidence of the 

 truth of my experiments. 



Since I published my paper in the Philosophical Magazine for Octo- 

 ber 1851, thermo-chemical researches have been extensively carried 

 on, and all based on the truth of the proposition I there proved, viz. 

 ** that decomposition of a compound body absorbs as much heat as 

 combination of the elements produced." Before that date no such 

 experiments were thought of, that is, the amount of heat produced 

 by the union of elements was in no instance calculated from any 

 process taking decomposition into account. The reason why the 

 combustion of a compound body, such as alcohol, does not produce 

 as much heat as the elements would when separately ignited, was 

 not even understood, — proofs that philosophers were not aware of 

 the principle before my paper was published, and consequently had 

 not perceived it in Mr. Joule's. 



I published a paper in the Philosophical Magazine for November 

 1852, proving that tlie intensity of the affinity of elements for oxy* 

 gen might be measured by the quantity of heat their combination 

 with that body produces. On referring to Mr. Joule's paper pub- 

 lished in vol. XX. of the Philosophical Magazine for 1842, I find that 

 he has there proved the same proposition. If I had known of this 

 paper when I published mine, I would have quoted it in preference ; 

 but at the same time I must say, that if the proposition hQ true and 

 of importance, I have a right to claim its establishment ; for although 

 Mr. Joule in 1842 brmgs it forward, in 1843 he rejects it. (See 

 Phil. Mag. vol. xxiii. page 442.) It was therefore the more necessary 

 subsequently to show it was correct. 



I have the honour to be. 



Your obedient Servant, 



Thomas Woods. 



. . - ON HEAT AS THE EQUIVALENT OF WORK. 



Hoppe has contributed a memoir upon this most interesting and 

 important subject, which places the analytical theory in a remarkably 

 clear, simple, and general point of view, so far at least as it relates 

 to permanent gases. We shall give the author's investigation in 

 extenso, making however a slight change in the symbols employed, 

 so as to assimilate them to those usually employed by writers on 

 the calculus in French or English. The temperature r of an enclosed 

 permanent gas may be expressed as a function of the pressure p, 

 and the volume v by the following formula, which is a combination 

 of the laws of Gay-Lussac and Mariotte : — 



pt,= ^a+ar). (1) 



In this formula m represents the mass of the gas, a any definite 

 pressure, that of one atmosphere for instance, h the density at the 

 temperature 0° and pressure a. If we consider the temperature to 



