On the Contraction of Water ly Hat. 165 



•did pass from the lower strata upwards, hut extremely 

 slowly, by reason that tiuids, as Count Ruuiibnl taught 



us, 



myself that he assioT.ed to fluidity a character that docs not belong- to it. 

 Though since the date oi these experiments, the public h tn become poisesse(^ 

 of several series, well devised, and, in my opinion, of thi/niselves conclusive, 

 it may yet be worth while to state the tenor ai\d result of them, by which 

 the value of their testimony in favour of the conducting power of li(juids 

 may be estiinated- 



The experiments were of two descriptions. 



The one set, ot the same nature nearly with those of Count Rumford, 

 was designed to examine, Whether heat, when applied to the surface, can 

 descend in a fluid ; and the other, to discover, Whether, on the mixture of 

 different portions of fluid at different temperatures, an interchange of caloric 

 takes place between the particles ; — Water, oil, and mercury, having been 

 the subjects of the Count's experiments, were employed for the first set. 



To explore the conducting power of water and oil, the apparatus which I 

 used consisted of two vessels of tinned iron, both cylindrical, and the one 

 somewhat larger than the other. The larger had a diameter of eleven inches, 

 2.nd into it were poured the subjects of the trial, to dilJcrent depths on dif- 

 ferent occasions. The smaller was ten and a half inches in diameter. By 

 three hooks it was suspended within the larger pan, ia such a manner that 

 the bottom of it exactly reached and came in contact with the surface of 

 the fluid. Thissmalier vessel became the source of the heat, by being filled 

 with boiling hot water. The water was changed frequently, care being 

 taken to avoid, by the use of a syphon, all agitation and disturbance. 



In experiments of this nature, the difficulty is to prevent the conveyance 

 of caloric by tile sides of the vessel. 1 attempted, and, I think, I succeeded, 

 in overcoming thtsxiifliculty,by encircling the larger vessel, at a height ex- 

 actly corresponding with that of the surface of the fluid within, with a gut- 

 ter or channel about half an inch in depth ; and bv causing a stream of cold 

 ■water to flow constantly through a svphon into this g-utkcr, while from the 

 opposite aide it ran orF by a small cpout. 



The water was sci'eral degrees colder than the subject of the experiment; 

 and keeping cool the portion of the vessel with which it was in contact, it 

 intercepted the heat that would otherwise ha% e traveUcd by tiiis route to the 

 bottom. 



For mercury I had recourse to vessels of glass. 



In all the experiments a thermometer bore testimony that the caloric de- 

 scended from the surface to the hi itiom of tjie fluid, and demonstrated, at 

 Jtast to my convictitjn, that fluids can conduct heat. 



Tlie progress of the heat, however, was viery slow, and attested the im- 

 portant fact, for which we ought to be thankful to tiie Count,.^ — ^'i'hat fluids 

 are very had conductors. 



The second set of experiments was calculated to examine, in a very dif- 

 ferent manner, the position. That all interchangeand communication uf heat 

 between the particles of fluids is impossible. 



When a hot and a cold fluid arc mixed togetlicr and well agitated, very 

 «oon an uniform temperature is pioducfcd. Thisequalilj must proceed eiilier 

 from a communication of heat from the warmer to the Culder fluid, agjce- 

 ably to the common opinion, or from a perfect intenuixlure of hot and coid 

 particles, according to the notion of Count Rmnford. To which cause it 

 ought to be atlributcd, 1 conceived I might discover, by asccruiining wlie- 

 ther, after such an iiilcnnixturo, any separ^itiou of the hot and cold por- 

 tions took place. If the njuilibiinm of leuiper.iture be owing m intermix- 

 ture without interchanjie ■.;f cakuic, the hotter particles, as soon as the agita- 

 tion ceases, ought, by reason of their greatti rarity, to acciurnilate to a cei- 

 tain degree, at the su>'face, aud there exhibit a tempciature above ihe com- 

 mon aat. 



h 3 I lirtt 



