160 On the Contraction of IVater ly Heat. 



assuming that situation which their specific gravity would 

 allot to them. 



It will appear, however, very clear, from the circumstances 

 of the experiments which I shall immediately detail, that no 

 obstacle to the success and precision of the experiments 

 proceeded from this source. 



It is not necessary for me to relate all the experiments I 

 have made. I shall restrict myself to the detail of six, 

 which present varieties in the modes of procedure, and 

 which aflbrd the most striking results. 



Experiment I. 



I filled a cylindrical jar of glass 8^ inches i\e:^, and 4-^ 

 in diameter, with water of temj^erature 32°, and placed it 

 on a tahle, interposing a considerable thickness of matter 

 possessed of little power of conducting heat. I suspended 

 two thermometers in the fluid, nearly in the axis of the jar, 

 one with its ball about half an inch from the bottom, tha 

 other at the same distance below the surface. The jar was 

 freely exposed to the air of the room, the temperature of 

 which was from CO" to 62°. 



The experiment commenced at noon : 



Top Thermom. Bottom do. 



32° - 32** 



In TO minutes, - 33+ - 34 + 



• — 30 - 33'5 - 37 



— 50 - 37 - 38 + 



— an hour, - 3S - 38 + 



■and I0minutes42 - 38'25 



30 44 - 40 



50 46+ - 41 + 



— 2 hours and 10 minutes 48 - 42-5 



30 50 - 44 



50 50-5 - 45 



— 4 hours - 54 - 49 

 Confiding in the indications of the thermometers, from 



this experiment, we learn, that when heat flows on all 

 sides from the ambient air into a column of ice-cold water, 

 the warmer portions of the fluid actually descend, and take 

 possession of the bottom of the vessel. 



This down'-'.ard course proclaims an increased density, 

 and testifies that the cold water is contracted by heat. As 

 soon, however, as the fluid at the bottom exhibits a tem- 

 perature of 3b°, this course is retarded and so(m stopped, 

 and with the rise of temperature beyond 40° is totally 

 changed : iox when the mass attains this degree, the expe- 

 riment 



