ON THE POWER OF FLUIDS TO CONDUCT HEAT. 57 



peared before — namely, that the quicknefs of the circulation and 



diffufion of heat in fluids, is occafumed principally by the internal 



motion arifmg from a change of Jpecific gravity qffeBed by the 



heat. — But the conclufion he has drawn from them — that fluids 



areperfed ?wn-conduclors of heat, in the way in which folids con- His Inference, 



dud it, appears to me totally unwarranted from the experi- ^.j^JXm 



ments, and erroneous in itfelf. And as it may be an error of erroneous, 



practical confequence, if adopted, the expofidon of it feemed 



defirable — which is the object of the following remarks and 



experiments. 



My firft attempt was to afcertain the precife degree of cold Experiments. 

 at which water ceafes to be further condenfed — and like wife 

 how much it expands in cooling below that degree to the tem- 

 perature of freezing, or 32°. For this purpofe I took a a thermometer 

 thermometer tube, fuch as would have given a fcale of 1 made with waler « 

 inches with mercury from 32° to 212°, and filled it with pure 

 water. I then graduated it by an accurate mercurial thermo- 

 meter, putting them together in a bafon filled with water of 

 various degrees of heat, and flirring it occasionally : as it is 

 well known, that water does not expand in proportion to its 

 heat, it does not therefore afford a thermometric fcale of equal 

 parts, like quickfilver. 



From repeated trials agreeing in the refult, I find, that the Greateft con- 

 water thermometer is at the loweft point of the fcale it is ca- ^ci™ at 

 pable of, that is, water is of the greateft denfity at 42^° of 

 the mercurial thermometer. From 41 Q to 44° inclufively the 

 variation is fo fmall as to be juft perceptible on the fcale ; 

 but above or below thofe degrees, the expanfion has an in- Law of expan- 

 creafing ratio, and at 32 ff it amounts to j-th of an inch, or 

 about -r^th part of the whole expanfion from 42°£ to 212° 

 or boiling heat. — During the investigation of this fubject, my 

 attention was arretted by the circumftance, that the expanfion . 

 of water was the fame for any number of degrees from the It Is the fame on 

 point of greateft condenfation, no matter whether above or eac . h b fi , de abo V oi 

 below it: thus I found that 32°, which are 10 o f below the 

 point of greateft denfity, agreed exactly with 53°, which are 

 IO°f above the faid point; and fo did all the intermediate 

 degrees on both fides. Confequently when the water ther- 

 mometer ftood at 53°, it was impoftible to fay, without a 

 knowledge of other circumftances, whether its temperature 

 was really 53 Q , or 32°. Recollecting fome experiments of 



Dr, 





