ACCOUNT OF A CURIOUS PHENOMENON. 211 



I wifbthat gentlemen who refufe their aOent to the opinions Recapitulatory 

 I have advanced rerpe6ling the caufes of this curious pheno- ^^ 

 menon, would give a better explanation of it than that which I ^ 

 have ventured to offer. I could likewife with that they would 

 inform us how it happens, that the water at the bottoms of all 

 deep lakes remains <ionftantly at the fame temperature : and, 

 above all^ how the cylindrical pits, above defcribed, are formed 

 in the immenfe maffes of folid and compact ice which compofe 

 the Glaciers of Chamouny ! 



A remark, which furprifed me not a little, has been madeby Notice of one re- 

 a gentleman of Edinburgh, (Dr. Thompfon,) on ^^^^ ^^P^^i- ^^^^^^yj^^' 

 ments I contrived, to render vifible the currents into which 

 liquids are thrown on a fudden application of heat, or of cold. 

 He conceives, that the motions obferved in my experiments, 

 among the fmall pieces of amber which were fufpended in a 

 weak folution of potafh in water, were no proof of currents 

 exifting in that liquid; as they might, in his opinion, have been 

 occafioned by a change of fpecific gravity in the amber, or by 

 air attached to it. I am forry that fo mean an opinion of ray 

 accuracy as an obferver (hould have been entertained, as to 

 imagine that I could have been fo eafily deceived. For nothing 

 furely is eafier, than to diftinguifli the motion of a folid fuf- 

 pended in a liquid of the fame fpecific gravity, which is 

 carried along by a current in the liquid, from that of a body 

 which defcends, or afcends, in the liquid, in confequence of 

 its relative weight, or levity. In the one cafe, the motion is 

 uniform ; in the other, it is accelerated. In a current, the body 

 may be carried forward in all directions, and even in curved 

 lines ; bat, when it falls in a quiefcent fluid, by the aftion of 

 gravity, or rifes, in confequence of its being fpecifically 

 lighter than the fluid, it muft neceflarily move in a vertical 

 direction. 



The fa6l is, that I very often obferved, in the courfe of 

 my numerous experiments, the motions of fmall particles of 

 matter, of different kinds, in water, which Dr. Thompfon 

 defcribes; but, fo far from inferring /rowz ^/jem the exiftence 

 of currents in that fluid, their caufe was fo perfedly evident, 

 that I did not even think it neceflary to make any mention of 

 them. 



I cannot conclude this Paper, without requefting that the 

 Hoyal Society would excufe the liberty I haye taken in troubling 



P 2 * them 



