Rivers durmg Winter. 131 



was obliged once a year to remove the stones and other foreign 

 bodies with which the channel became accidentally covered. 



In the beginning of February 1830, M. Duhamel, on, 

 breaking the ice which covered the surface of the Seine, a short 

 way below the bridge at Grenelle, about 10 feet from the banks, 

 found a layer of continuous ice 4 centimetres thick. He even, 

 procured many fragments. At this spot the water was upward* 

 of one yard deep. At every depth the thermometer stood at 

 zero centigr. The current was tolerably rapid. 



The experiment of M. Duhamel had this defect, like that 

 of Hales formerly mentioned, of having been made too close to 

 the bank. I could not, however, omit quoting it, as I am not 

 aware of any observation to be found elsewhere by a man of 

 science respecting the congelation at the bottom of the Seine. 



It has been mentioned already, that natural philosophers did 

 not believe in the formation of floating ice at the bottom of wa- 

 ter ; they ought, therefore, not to expect that any thing very 

 important will be found in the sketch I am about to present of 

 the theoretical speculations to which this theory has given rise. 



Sailors for the most part believe that the flakes of ice are 

 formed at night on the bottom of rivers, by the action of the 

 moon, and that it is the sun which attracts them to the surface 

 on the following day. Popular prejudices are generally ground- 

 ed on some imperfect observation. By recollecting what we 

 said concerning the red moon *, we shall easily discover how the 

 strange notion of which I have spoken arose. 



The theory of the sailors was not succeeded by an explica- 

 tion in any degree better. It was said that heat arises from the 

 rapid movement of the parts of bodies. The running water 

 flows less rapidly at the bottom than at the top, the maximum 

 of temperature is, of course, found at the surface ; it is at the 

 bottom, where there is the least agitation, that the congelation 

 ought to begin. To complete this theory, the ascension of the 

 flakes of ice was attributed to the elasticity which the air dis- 

 solved in the water resumes when it disengages itself during the 

 process of congelation, and to the formation, in the midst of the 

 icy mass, of bubbles of considerable size. 



• In the Scientific Intelligence of this Number, the reader will find some 

 account of the red moon mentioned above. 



