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ON THE GROUND-ICE OR THE PIECES OF FLOATING ICE OB- 

 SERVED IN RIVERS DURING WINTER. BY M. ARAGO. 



The severe winter of 1829-30 has attracted the attention of 

 natural philosophers to the phenomena of congelation in running 

 waters. They have examined how, and in what manner, im- 

 mense quantities of ice are formed which some rivers carry down 

 to the sea, and which, on being piled up against the arches of a 

 bridge, often cause fatal accidents. I confess that, in a theore- 

 tical point of view, the question does not yet seem, in my opi- 

 nion, to be exhausted. Is it not a strong reason, then, for my 

 presenting as complete an analysis as possible of the observations 

 to which it has given rise ? For want of a definitive solution of 

 so curious a problem, I shall at least have placed before the eyes 

 of meteorologists a complete tabular view of all the data with 

 which it is indispensable that the explanation shall agree. 



Every one knows that in a lake, a pond, in every sheet of 

 stagnant water, congelation proceeds from the exterior to the 

 interior. It is the upper part of the surface of the water which 

 is primarily affected. The thickness of the ice afterwards in- 

 creases in proceeding from above downwards. 



Is this the case with running waters ? Natural philosophers 

 are of this opinion. On the other hand, millers, fishermen, and 

 watermen, maintain that the masses of ice with which rivers 

 are crowded in the winter season, proceed from the bottom. 

 They pretend that they have seen them rise, and have often 

 borne them up with their hooks. They say, in order to 

 strengthen their opinion, that the inferior surfaces of large flakes 

 of ice is impregnated with mud ; that it is encrusted with 

 gravel ; that, in short, it bears the most unequivocal marks of 

 the ground on which it rested ; that, in Germany, the sailors 

 have a peculiar and characteristic term to designate floating ice 

 which they call grundeis, i. e. ground-ice. Such arguments 

 make little impression on prejudiced minds. It would require 

 nothing less than the evidence of many experienced philosophers 

 to cause a belief in the reality of a phenomenon which seems di- 



