754 LECTURE LX. 



years by the Royal Society to the author 6f the most valuable discovery re- 

 specting heat or light, forms an era less remarkable, than the first adjudication 

 of the medal to himself, and the second to Mr. Leslie. Count Rumford's nu- 

 merous experiments, on the production and communication of heat are highly 

 important, both for the utility which may be derived from their economical 

 application, and for the assistance which they afford us in the investigation 

 of the intimate nature of heat. Mr. Leslie's discovery of the different pro- 

 perties possessed by surfaces of different kinds, with regard to emitting and 

 receiving radiant heat, is in every respect highly interesting; and the multi- 

 plicity and diversity of his experiments would have entitled him to still 

 higher commendation than he has obtained, if they had been more simply and 

 circumstantially related. Perhaps, however, none of the modern improvements 

 in speculative science deserves a higher rank than Dr. Herschel's discovery of 

 the separation of heat from light by refraction. Mr. Prevost has made some 

 just remarks on the experiments of other philosophers respecting heat; and 

 his own theory of radiant heat, and his original investigations, on the effect of 

 the solar heat on the earth, have tended materially to illustrate the subject of 

 his researches. 



The general laws of the ascent and descent of fluids in capillary tubes, and 

 between plates, of different kinds, had long ago been established by the ex- 

 periments of Hauksbee, Juvin, and Musschenbroek; many other circum- 

 stances, depending on the same principles, had been examined by Taylor, 

 Achard, and Guyton ; and some advances towards a theory of the forms as- 

 sumed by the surfaces of liquids, had been made by Clairaut, Segner, and 

 Monge. In an essay on the cohesion of fluids, read before the Royal Society 

 in the year 1804, I have reduced all effects of this nature to the joint opera- 

 tion of a cohesive and repulsive force, which balance each other; assuming 

 only that the repulsion is move augmented by the approach of the particles to 

 (?ach other than the cohesion ; and I have had the satisfaction of discovering 

 i^ this manner a perfect correspondence between many facts, which had not 

 l?een supposed to have the slightest coanexion with each other. Alinost a 

 year after the publication of this paper, Mr. Laplace Fcad to the National In- 

 stitute a memoir on capillary tubes, in which, as far as he has pursued the 

 subject, he has precisely confirm«d the most obvious of my concLusicns; 



