82 ON THE SUPPOSED CURRENTS IN HOT LIQUIDS. 



Concifcnairatlve Count Rumfbrd was firft led to fufpect that fluids are non* 

 ford'Texperi- " conductors of caloric, by the appearance of certain opaque 

 ments to render particles moving upwards and downwards in them, while they 

 abl"'^^^^^" WCre coolIn S in :i window, cxpofed to the direft light of the 

 by floating grains fun. He very naturally concluded that thefe motions were 

 of amber. occafioned by the currents of the liquid moving in the fame 



direction with the opaque bodies. Hence he inferred that 

 every individual particle of the liquid was cooled only by de- 

 positing its caloric at the furface or '.he fides of the veftel, and 

 that therefore thefe particles were incapable of giving out heat 

 to each other. The contrivance by which he rendered thefe 

 motions vifible to the naked eye was in the higheft degree 

 Ample and ingenious. He mixed amber, in the ftate of fmall 

 grains, with an alkaline folution, diluted with water till its 

 fpeciiic gravity was exactly the fame with that of amber. 

 The amber, of courfe, remained fufpended in any part of the 

 liquid ; but as foon aS heat wits appli«d, it began to move 

 upwards and downwards, exhibiting the currents to the eye 

 of the fpectator. 

 The motions of ' Nothing can appear a more fatisfactory proof of the ex- 

 aW^eeii ^ ^ ence °f currents in the liquid than the motion of the amber ; 

 thought demon- lb convincing is it indeed, that hitherto no perfon, as far as I 



Sncfofcur- know > has ever ml *P e ^ cd th « poffibility of this motion ori- 

 ents | ginating from any other caufc. I have repeated the experi- 

 ment frequently, and even exhibited it to others ; and though 

 the motions did not exactly correfpond with thofe indicated by 

 Count Rumford., they never failed to produce the fulleit con- 

 viction of the exigence of the very currents which that phi- 

 but they are not fofopher had indicated. Yet the fact is, that the motion of 

 ™entu * CUr ~ ^ re amDer 1S no1t occafioned by currents in the liquid, and 

 Very often exiits when there are really no currents at all. * 

 This aflertion will probably, at firil feht, appear rather ex- 

 traordinary ; but tire proofs on which it is founded leave no 

 room for doubt. 

 Difficulties at- When we reflect upon thefe fuppofed currents, feveral 

 pofltion ofcur-" cXnClijpfianjCes cannot fail to prefent themfelves, which do not 

 rents as rapid as admit of an eafy explanation. Tlve motion oi' the amber i? 

 the ISJberT ° f prett ^ ra P id> ^ Ct the inerc difee « ce W the *P«cific gravity of 



* I negle& the trifling currents occafioned by the amber itfelf, 

 which it would be extremity difficult to appreciate. 



the 



