288 Inquiries concerning the Mode of the 



it is also easy to prove, from the inflection which light experiences in 

 passing over the surface of an opaque solid body, that a considerable 

 quantity of opaque solid matter could be held suspended in water 

 without sensibly diminishing its transparency, and without changing its 

 colour; that is to say, without giving any indication of its presence.* 



"I have long suspected that the suspension of solid substances which 

 are held in solution by liquids is due solely to the imperfect fluidity of 

 the solvents, and the results of a great number of experiments which I 

 have made to elucidate this important subject have always confirmed 

 this opinion. Since, then, bodies specifically heavier than water can 

 nevertheless remain suspended in that liquid, there can be no difficulty 

 in admitting that isolated particles of cold water can equally remain 

 motionless in the warm water with which they find themselves acci- 

 dentally mixed. But although this may be true of the individual par- 

 ticles, the same principle cannot apply to masses of sensible size made 

 up of a great number of these particles. These masses must yield to 

 the natural effect of the differences in their specific gravity, and form 

 currents which will be ascending or descending according as the masses 

 in question are warmer or colder than the surrounding liquid; and 

 these currents must contribute very largely to the intimate mixture of 

 the particles at different temperatures, and must soon bring about a cer- 

 tain uniform temperature throughout the entire mass of the liquid. 



" I said this uniformity of temperature may be only apparent ; because, 

 if water is really a perfect non-conductor of heat, the particles of cold 

 water, at least those which have not been warmed by contact with the 

 walls of the vessel in which they are contained, ought to remain cold 

 in spite of their more or less intimate mixture with the warm particles; 

 but, notwithstanding this fact, the mean temperature of the liquid, as 

 shown by the thermometer, will be precisely the same as if there had 

 been an actual communication of heat among the particles. 



" Long after I had had reason to persuade myself that all the heat ac- 

 quired by liquids, when they are warmed, is communicated by the ves- 

 sel containing them to the individual particles, which are successively 



* In order to satisfy my curiosity, I found, by calculation, the diameter which a 

 small solid spherule of gold ought to have in order to its remaining suspended in 

 water in consequence of the viscosity of that liquid. I found this diameter to be 

 j , or, in round numbers, of an inch ; that is to say, about two hundred 

 times smaller than the diameter of a single fibre of raw silk, as spun by the worm, 

 an object which is so fine as scarcely to be visible. 



