Propagation of Heat in Liquids. 287 



[THE preceding paper is printed from Nicholson's Journal, XIV. 

 (1806), pp. 355- 363. The paper, in a somewhat modified form, ap- 

 pears in the Bibliotheque Britannique (Science et Arts), XXXII. ( 1 806), 

 pp. 123 141, to which periodical it was contributed by Count Rum- 

 ford in manuscript, which was translated by the French editor. In 

 this version the beginning of the paper is much abridged ; but in the 

 latter part Rumford elaborated his speculations in regard to the effects 

 produced by viscosity on the propagation of heat in liquids more at 

 length than in Nicholson's Journal. In order to give fully his views 

 on the subject, this portion of the French paper is here appended. 



"If there is no direct communication of heat between contiguous par- 

 ticles of water at different temperatures, then the apparent mean tem- 

 perature, which results so quickly when cold water is poured into a 

 mass of warm water, must be produced by currents caused by differ- 

 ences in the specific gravity of the masses of the liquid at different tem- 

 peratures. And if it is asked why the hot and cold particles, thus mixed 

 together, do not separate again, on account of the difference in their 

 specific gravity, we must seek for the reason in the imperfect fluidity of 

 the water. This cause may keep the particles of water suspended, out 

 of their natural position, just as it keeps in suspension, as well in other 

 liquids as in water, particles of foreign substances, which, although 

 specifically heavier or specifically lighter than the medium, are so small 

 that the amount by which they are heavier or lighter than the surround- 

 ing liquid is not sufficient to overcome its viscosity. 



" This want of perfect fluidity, a condition common to all liquids in 

 different degrees, gives rise to a great number of very interesting phe- 

 nomena, and it is a subject worthy of the close attention of philosophers. 



" From the result of an experiment which I made a long time ago in 

 order to determine the measure of the viscosity of pure water at the 

 temperature of 64 F., that is the force necessary to separate contigu- 

 ous particles of that liquid, I found reason to conclude that a solid body, 

 having a surface equal to 368 square inches, which should weigh only 

 one grain Troy more than an equal volume of water, would remain sus- 

 pended in that liquid ; and from this datum it is easy to find, by calcu- 

 lation, what ought to be the diameter of a small solid spherule of the 

 heaviest matter, of gold, for instance, in order to its remaining 

 suspended in water in consequence of the viscosity of that liquid : and 



