100 Observations on Radiant Heat. [Avd. 



duced from the combustion of hydrogen gas by a jet of oxygen ; 

 but the process was attended with some inconvenience and diffi- 

 culty, and the effects, I believe, fell short of those just described. 

 1 remain, dear Sir, yours, &c. 



Alkx. Marckt. 



Article V. 



Observations on Radiant Heat. By F. Delaroche, M.D.* 



I proposk in this memoir to state several propositions which 

 appear to me capable of throwing some light on the theory of 

 radiant heat ; and which, I think, I have established by decisive 

 experiments. These experiments, indeed, were made with 

 sufficient care to prevent any doubts about their exactness ; but 

 I may be deceived in the conclusions that I deduce from them. 

 In that case I shall readily acknowledge my error j nor shall I 

 think that I have lost my labour if I draw, upon so interesting a 

 subject, the attention of some philosopher more fortunate than 

 myself, or better situated for examining it with accuracy. 



First Proposition. — Invisible Radiant Heat may in some 

 Circumstances pass directly through Glass. 



Different philosophers, and particularly Mr. Leslie, conceive 

 that they have proved the falsehood of this proposition ; but the 

 experiments of Professor Prevost, of Geneva, have lately esta- 

 blished its truth in an incontestable manner. He obtained his 

 result by separating the immediate effects of transmitted heat 

 from those produced by the heating of the glass, by a process 

 equally simple and ingenious ; namely, by employing moveable 

 screens of glass, which he renewed continually, and of course 

 did not give them time to become heated. I have myself, since 

 I became acquainted with the memoir of M. Prevost, made a 

 great many experiments, which appear to me to prove the same 

 thing. The nature of these will be stated in support of the 

 second proposition. 



Second Proposition. — The Quantity of Radiant Heat which 

 passes directly through Glass is so muck greater relative to the 

 whole Heat emitted in the same Direct ion, as the Temperature of 

 the Source of Heat is more elevated. 



M. Delaroche shows, in the first place, by some ingenious 

 oxperiments, that a thermometer (of the temperature of the 



v Abridged from the Journal de Physique, vol. lxxv. p. 201. 



