AT THE BOTTOM OF THE WATER. 427 



zero, and wlien plungetl one or two feet deeper ascended to 3A above zero. 

 Proceedinji; to the end of the embankment, at a .«liort dit^tance from u very rapid 

 current, and in a sort of inlet -where the water had at first but liltle depth, I saw 

 all the pebbles covered Avith a kind of transparent moss from an inch to an incli 

 and <i half in thickness, composed of crystals of ice combined in every manner ; 

 a true crystallization in effect, pron-.olted by the presence of the pebbles, and iu 

 all respects similar to that which is furnished by certain salts in our laboratories. 

 I'he thermometer indicated zero at this ]ioint, as Avell towards the border as at 

 a depth of several feet, in the most rapid })art of the current. We were presently 

 able to distinguish in this latter part, at a depth of about five feet, large masses 

 of this spongy ice into which an oar could be thrust with the greatest facility, 

 and portions which Averc thus detached were found to be exactly similar to in- 

 numerable fragments of ice which were then drifting in the river." 



Hence M. Fargeaud concludes : " 1st, that in rivers having a greater or less 

 depth and no current the water will long maintain a temperature above zero, 

 whether from the warmth of the ground or the small conductive capacity of the 

 water, or, in fine, from the very fact of the species of e(|uilibrium which results 

 from the maximum of density. AVhen such a river freezes, the ice must of ne- 

 cessity form at the surface ; 2dly, that if, on the contrary, the current be very 

 rapid, the whole mass must be brought to zero ; 3dly, that the water thus 

 brought to zero may preserve for some time its liquid state, especially on a bot- 

 tom of ooze or sand, but that in general it Avill be disposed to crystallize, and 

 will in fact crystallize wherever any cause shall contribute to produce this change 

 of condition." 



M. Fargeaud then adds, in allusion to the facts Avhich I had stated in his 

 presence in the Strasbourg Society of Natural History, " that he had learned 

 that a superintendent of the forges of the Vosges, in order to prevent the ice 

 from forming at the bottom of the stream Avhiclr supplies his works, had caused 

 the stones and other extraneous bodies found therein to be removed every year." 

 My experiments were afterwards cited by Arago and other physicists with sim- 

 ple reference to a " master of the forges of the Vosges." 



Berzelius, in his Comptc Rendu for 1829, also speaks of the ice at the bottom 

 of rivers ; he had himself seen the jjhenomcnon but once. He reports the ob- 

 servations of Hugi and a letter of M. Heaucourt, published in the Glohc of the 

 17th February, 1830. 



Arago, in the Annuairc du Bureau des Longitudes for 1833, relates all that 

 was then known respecting ice at the bottom of the water, and gives the following 

 explanation of it : " Who does not know that in order to hasten the formation 

 of crystals in a saline solution, it is sufficient to introduce into it a body either 

 pointed or of uneven surface ; that it is especially around the asperities of bodies 

 that crystals take their origin, and receive rapid accretions ? The same, we may 

 be assured, is the case Avith the crystals of ice. 



" liut what we have just said," he continues, "is not precisely the process in 

 the congelation of rivers ; this Avill scarcely be suspected, I think, if we remem- 

 ber that the congelation never occurs on the bed itself except Avhere rocks, peb- 

 bles, pieces of wood, plants, &c., exist. Another circumstance which seems 

 capable also of playing a certain part in this phenomenon is the movement of 

 the water. At the surface this movement is very rapid and sudden ; it must, 

 therei'ore, tend to obstruct the symmetrical grouping of the needles in that po- 

 larized arrangement, Avithout Avhich crystals of Avhatever nature acijuire neither 

 regularity of form nor solidity; it must often break the crystallized nucleus, 

 even in its rudimentary state. 



" Movement, that great obstacle to crystallization, if it exist at the bottom as 

 at the surface of the Avater, is there at least greatly diminished. It may be sup- 

 posed, therefore, that its action Avill only confiict Avith the formation of a regular 

 or compact ice, but Avill not prevent in the end a multitude of small filaments 



