[BARNES J ANCHOR-ICE P^ORMATION 81 



mix all the layers. The hydrostatic order on which we have insisted 

 so much is overthrown. The water, then, which is lightest does not 

 always tloat ou the surface. The currents are precipitated into the 

 general mass, which is therehy cooled, and whose temperature soon 

 becomes equal throughout. 



'J'o repeat, in a deep mass of stagnant water, the temperature of 

 tlie bottom can never descend below -{- 4"" cent. When this mass is in 

 a state of agitation, the surface, the middle, and the bottom, may be 

 found at zero simultaneously. 



"\A^e have only now to examine, why, when this uniformity of tem- 

 perature exists, and when the entire liquid mass is at zero, that con- 

 gelation commences at the bottom, and not at the surface. 



But where is the person who does not knov/, that to produce a 

 speedy formation of crystals in a saline solution, it is merely necessary 

 to introduce a pointed body, or an unequal surface into it; that it is 

 around the asperities of such a body that crystals originate and are 

 promptly increased? Be it so, every one may be assured that this is 

 the case with crystals of ice ; that if the mud in which the congelation 

 occurs presents a rent or projection, or solution of continuity of any 

 kind, it will become as so many centres, around which the filaments of 

 frozen water will prefer to arrange themselves. 



But is not what we have said exaplly the history of the freezing 

 of rivers? This cannot be doubted, if we recollect, that it never takes 

 place in the channel, unless where there are rocks, stones, pebbles, 

 pieces of wood, herbs, etc. 



There is another circumstance which seems to have a certain share 

 in this phenomenon, viz., the motion of the water. At the surface 

 this motion is verv^ rapid and irregular; it ought, of course, to put a 

 stop to the symmetrical grouping of needles ; to that polar arrangement 

 without which crj^stals, Avhatever be their nature, can neither acquire 

 regularity of form, nor solidity; it should, of course, frequently break 

 the crystalline groups, even in their rudimentary state. 



This motion, which is the principal obstacle to crystallization, 

 if it exists at the bottom as well as the surface of the water, is at least 

 greatly diminished at the former. It may be supposed, therefore, 

 that its action will merely oppose the formation of regular or com- 

 pact ice, but will not eventually prevent a multitude of little filaments 

 becoming irregularly blended, and thus produce that kind of spongy 

 ice through which M. Hugi so easily drove the oars of his boat. 



Having proceeded thus far, the reader may ask why T did not 

 present what preceded, as a complete explanation of the formation of 



Sec. III., 1906. 6 



