^^4 Congehtton at tht Hotiom tf Waitr.'-Grovni leh 



ftirface to cffecl their congelation. Whether this fyppofition may agree with the affuaJ' 

 ftate of things or not, might perhaps be afcertained by reafoning from former fa£ls ; but in alli 

 fuch quefHons where tbedecifion can be immediately and fimply haci from experiment, it. is 

 certainly bed to apply to that fource of information. Coimt Rumford made the trial, by 

 pouring mercury into a glafs tumbler to the depth of one incbj and upon this about the fame 

 bulk of water. Both fluids were at the temperature of 60 degrees. The tumbler was then 

 placed in a freezing mixture of fnow and common fair, which reached no higher than the 

 upper furface of the mercury. The ice was formed at the bottom in contact with the mer- 

 cury, not only under thefe circumftances, butalfo when the experiment was varied by pre- 

 vioully cooling the mercury to about ten degrees, and then gently pouring boiling hot water 

 on its furface. This laft fluid was inftantly frozen, and gradually formed a thick cake of, 

 ice, covering the mercury, though almofl the whole of the mafs of the unfrozen water which; 

 rcfted on this ice remained nearly boiling hot. 



Among the inferences deduced from this experiment, Count Rumford makes one, to ac- 

 count for the formation of ice at the bottom of rivers, which he thinks can only take place 

 in fuch ftreams as do not conftantly fill their bed, but occafionally overflow portions of 

 ground cooled by the atmofphere below the freezing point*. Another important inference ' 

 from the fame fcfts is, that it is impoflible any fluid fliould be of the fame temperature while 

 expofed to light, though its mafs be everfo fmall, and that atthediflerence of heat muft occa-. 

 fion perpetual motions among its parts.. This confequence is very fully explained in detail by 

 our author, who confiders fluidity as the life of inanimate bodies, and congelation as the 

 lleep of death ; and is thence difpofed to reje£t altogether the attribution of attractive powers 

 or exertions of any kind to dead motionlefs matter. He extendshis meditations to the vital 

 principle in living animals, and demands whether their life alfo do not depend on the internal 

 motions in their fluids occafioned by an unequal diltribution of heat ? and whether {Emula- 

 tion be not in alb cafes the mere mechanical efFcdl of the communication of heat ? — The an- 

 cient hypothecs, that the life of an animal reGdes in its blood ; the evident teadency of re- 

 ^iration, digeftion,, and infenfible perfpiration to produce and perpetuate inequalities of tem-- 



* I am not acquainted with th'" peculiar circumftances under which ground ice is formed ;. but it is certain- 

 1/ poflible that fuch an event (hould happen in a ftream which conftantly filli its banks. Snppofc a ftream to 

 flow with very little agitation in contaft with an atmofphere eight degrees or more beneath the freezing point. 

 It is known that water whofe parts are relatiTely at reft, or nearly fo, may be xoolcd about eight degrees below 3i»' 

 without affuming the folid ftate. The middle of our ftream might therefore continue fluid when fo cooled, 

 and the congelation would only take place at the fides, where the friflion againft the banks would caufe the 

 rcquifite internal agitation. The middle cold ftream, on account of its expaafion beneath 41 degrees, wouM^ 

 occupy the furface, and confequently could not rub againft the bottonv except in fliallow places, or unlefs fome 

 means were to offer of fuiking it. Suppofe one or more fprings rifing from a great depth in the earth, and, 

 thence poffelfing the mean temperature of the climate, to flow into the principal ftream. This mafs of warm 

 water would occupy the fuperior part of the ftream, and caufe the cold mafs to defcend; and wherever this 

 touched the-bottom it would be agitated, and form a coat of ice. Thefe effefts would be governed by the 

 temperatures, the maflfes, and the local requifites, for which upon the whole we are in want of obfcrvations. A»- 

 10 the aflTumed fafls, they are undoubtedly poffible. A remarkable inftance of a warm ftream in winter it feen ^ 

 in the fmall river Wandle, which burfts out of the earth near Carftalton in Surrey, and after flowing with con- 

 fderable velocity over a line of ten miles, and giving aftivity to thirteen mills, falls into the river Thames at. 

 Wandlworth wifhoHt having had time to acquire the freexing temperature, even in the fevercft weather. N. 



peraturej, 



