250 Biographical Account of Sir B. Thompson^ Knt. [Aphil, 



exposed to tlve ra^'s of the sun they undergo remarkable changes. 

 Thus the oxides of gold and silver, if in contact with combustible 

 bodies, are reduced; chlorine and hydrogen gas explode, and form 

 muriatic acid ; water iiolding chlorine in solution emits oxygen gas, 

 &c. Count Rumford suspected that these effects were occasioned 

 solely by the heat evolved by the absorption of the light. The 

 experiments lelated in this paper were instituted in order to deter- 

 mine the point. Though they cannot be considered as quite satis- 

 factory, yet it seems established by the subsequent experiments of 

 chemists, particularly of Gay-Lussac and Thenard, that the opinion 

 entertained by Count Rumford on this subject is correct. 



11. An Inquiry concerning the Weight ascribed to Heat. Phil. 

 Trans. 1799. P. 179- — From an experiment of Dr. Fordyce, it 

 was concluded that bodies become heavier the more they are cooled, 

 and of consequence that heat diminishes their weight. But Count 

 Rumford found, on repeating the experiment, that the supposed 

 increase of weight was a deception, arising from vapour condensing 

 on tlie surface of the glass vessel in which the experiment was 

 made. Lavoisier had previously ascertained the same thing. 



It does not seem necessary to give a particular account of the 

 remainder of Count Rumford's writings. His two volumes of essays 

 are of a very miscellaneous nature, and the most important of the 

 essays are republications of those papers which have been already 

 noticed. The seventh essay, in which the Count endeavoured to 

 prove that fluids are nonconductors of heat, has been sufficiently 

 refuted by the more decisive experiments of subsequent chemists. 

 Indeed the Count himself, though abundantly obstinate, appears at 

 last to have given up his opinion. The essays on the treatment of 

 the poor, on cooking, on chimnies, and on the management of 

 fuel, are not very susceptible of abridgment. His paper published 

 in the Philosophical Transactions for 1804, entitled, An Inquiry 

 concerning the Nature of Heat and the Modes of its Communica- 

 tion, gives us a number of curious facts respecting the effect of 

 surface on the heating and cooling of bodies. But the publication 

 of Mr. Leslie's book on heat, in which this subject is treated of at 

 much greater length, and much more completely, have deprived 

 this essay of most of its interest. It is not necessary to notice the 

 papers published by the Count in Nicholson's Journal for 1805. An 

 outline of his last paper. On the Quantity of Heat evolved during 

 the Combustion of different Bodies, was given in the first paper in 

 the third volume of the Annals of Philosophy, to which I beg 

 leave to refer the reader. 



