256 Account of a curious Phenomenon 



of it than that which I have ventured to offer. I could 

 likewise wish that they would inform us how it happens 

 that the water at the bottoms of all deep lakes remains 

 constantly at the same temperature ; and above all, how 

 the cylindrical pits above described are formed in the 

 immense masses of solid and compact ice which compose 

 the glaciers of Chamouny. 



A remark, which surprised me not a little, has been 

 made by a gentleman of Edinburgh (Dr. Thomson), 

 on the experiments I contrived to render visible the 

 currents into which liquids are thrown on a sudden 

 application of heat or of cold. He conceives that the 

 motions observed in my experiments, among the small 

 pieces of amber which were suspended in a weak solution 

 of potash in water, were no proof of currents existing in 

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

 occasioned by a change of specific gravity in the amber, 

 or by air attached to it. I am sorry that so mean an 

 opinion of my accuracy as an observer should have been 

 entertained, as to imagine that I could have been so 

 easily deceived. For nothing, surely, is easier than to 

 distinguish the motion of a solid suspended in a liquid 

 of the same specific gravity, which is carried along by a 

 current in the liquid, from that of a body which descends, 

 or ascends, in the liquid in consequence of its relative 

 weight or levity. In the one case the motion is uni- 

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

 body may be carried forward in all directions, and 

 even in curved lines ; but when it falls in a quiescent 

 fluid by the action of gravity, or rises in consequence of 

 its being specifically lighter than the fluid, it must neces- 

 sarily move in a vertical direction. 



The fact is, that I very often observed, in the course 



