tONtRACTlOtt OF WAtER BY HE A*. 5.55 



Bottom. Top. 



In 20 minutes, 3S° — 38° — 



— 30 — 3? — 37— 



— 40 36 36 



— 60 — i 35.5 35.5 



— SO — 35 35 



— 100 3J-.5 35 



. 120 34— 34 



— 8 hours, 34- — 34 



A cruft of ice began to form on the inlide of the glafs 

 'when the water in the axis of the bottom and of the top was 

 at 36°. In the courfe of the experiment, it became at leaft 

 an inch thick. 



We learn from this'experiment, that cold applied tothe lower 

 part of a cylinder of water, nearly 18 inches long, and having 

 the temperature of 40?, is actually as fpeedily perceived at the 

 fummit as in the axis of that part, on the external furface ofwhenceitis 

 which it immediately afts. As fluids condud heat fo very tar- ^^ ^ ef 

 dily, this can only arife from currents of cooled water afcend- attended from 

 ingfrom the bottom, and thefe cold currents cannot move up- * he bottona fro . m 



its greater rarity 



wards, were not the water of them fpecifically lighter than that below 40°; 

 ©f the incumbent warmer fluid. 



The water, therefore, which at the bottom is cooled by the 

 contiguous frigorific mixture, muft be expanded by the lofs of 

 caloric. 



This experiment fecures full force to the laft, as it obviates and the objec- 



the objection already noticed, and alfo precludes another. I t,ons t0 Ex P' 3 ' 



J r arc removed, 



have already ftated, that it may perhaps be alledged, that 



the fluid at the top, in experiment third, though cooled 



to 32° did not defcend, becaufe below 40 Q , the contraction 



is fo trifling, that it does not occafion a difference of-fpe- 



cific gravity fufficiently great to caufe the particles to defcend, 



when oppofed by the inertia and tenacity of the fluid through 



which they have to fall : or it may be conceived, that the 



defcent is fo tardy, that time is given to the ambient air or 



fubjacent fluid to furnifh heat enough to raife the temperature 



of the defcending (bream, and by that arreft it in its downward 



courfe. 



But from the particulars above recorded, it is manifeft, that 



the change of denfity between the temperature of 32° and 



4-0° is quite fufficient to put into motion the particles, and to 



A a 2 enable 



