82 EOYAL SOCIETY OF CANADA 



the gnmcl-eis of Germany, of the glaces de fond of our sailors. This 

 is my answer: 



We have no observations which prove that this kind of ice is seen, 

 "until the temperature of the whole of the water is at zero. It is 

 not certain that the little icy particles floating on the water, mentioned 

 by Mr. Knight, and which may have acquired, by coming into contact 

 with the air, at least on their upper surface, a temperature considerably 

 below zero, do not play an important part in this phenomenon, which 

 I have entirely overlooked; that, viz., of cooling the stones covering 

 the bed of the river, when dragged thither by currents. Is it not 

 possible that these floating filaments were the principal elements of 

 the spongy ice which was afterwards to be formed? 



Our theory does not explain in what manner this ice, once formed, 

 only increases in a downward direction. If the remark of Desmarest 

 be correct, there is something wanting to complete it. 



During the congelation of the bottom of the Aar, at the place 

 where the ice is formed, M. Hugi immersed pitchers filled with hot 

 and cold water. The frst, he says, on l^eing brought up, was covered 

 with a layer of ice of one inch thick, the other had no marks of con- 

 gelation. Bullets covered with cloth, warm as well as cold, afforded 

 similar results. 



These remarkable experiments cannot be kept out of view. They 

 ought to be repeated in a variety of ways: we should be sure whether 

 these two bodies, on being immersed, do not differ but in temperature; 

 that their surfaces are equally polished; and if, after all the minute 

 precautions with which an able philosopher is sure to avail himself, 

 it be found that the body, originally hot at the moment of immersion, 

 is covered, as we are assured by M. Hugi, with more ice than the cold 

 one, it will, perhaps, be necessary to attribute this singular phenomenon 

 to the internal movement of the liquid; to currents which, being caused 

 at first by the presence of a hot body, still continued after it became 

 cold; to currents which incessantly continued to throw over this cold 

 body filaments frozen on the surface. 



Before coming to the conclusion, that the question which we have 

 been discussing is completely solved, it would be necessary to subject 

 the texture of the ices at the bottom to additional experiments; we 

 must ascertain accurately whether the vesicular cavities, which tra- 

 verse it in every direction, contain any air, — or if they are completely 

 empty, — for this circumstance is very necessary, in order to enlighten 

 us as to the place where they originate. 



I am expatiating, however, beyond my plan. I at first merely 

 wished to examine, whether the floating ice was produced at the bottom 



