13d On ifie Ground Ice observed in 



1".3, — .9°.4. That of the water, at 5 centimetres deep, 0^0 ; 

 at 1°».8, +1°.0 ; at 0"^.5 from the bottom, +1°.5 ; at the bottom, 

 +2°.4; at 1°*. in the ground, +8°.0. 



These determinations of the temperature of the water were 

 obtained in a part of the river which had no ice at the bottom. 



M. Fargeau, a distinguished professor of natural philosophy 

 in Strasbourgh, has made some observations on the Rhine, 

 which have been communicated to the Academy. Notwith- 

 standing what we have read, they are very deserving of notice. 



On the 25th of January 1829, at 7 o'clock a. m., the tempe- 

 rature of the air, near the bridge of Kehl, was at 13°.71 centigr. 

 At the same moment, in that part of the Rhine, which, owing 

 to the situation of its sand-banks, formed, on the French side, a 

 sort of lake witJiout currents^ the water of which was at zerOy 

 but at the depth of | metre it was -|-4°.4 This place had only 

 a few plates of ice near the banks. 



Beyond the banks of sand, in a little creek where the shal- 

 low water was co7itiguoits to a very rapid current, all the peb- 

 bles seemed covered with a sort of transparent mass of from 3 

 to 4 centimetres in thickness, and which, on examination, was 

 found to consist of icy spicula crossing each other in every di- 

 rection. In this creek the thermometer stood at zero cent, both 

 at the surface and at the bottom of the water. It was the same 

 even in the most rapid part of the current. There was also 

 seen, either in the channel of the Rhine, or on some pieces of 

 wood on the side opposite to the current, at a depth of 2 metres, 

 large masses of spongy ice, into which the pole of a waterman 

 entered with ease. This ice, on being borne to the surface of 

 the water, was found closely to resemble the innumerable flakes 

 which were at that time floating on the surface. M. Fargeau 

 states, that he saw ice on many occasions with his own eyes, in 

 the greater Rhine, separate from the bottom, and rise to the 

 surface. 



M, Fargeau has added an important observation to his own 

 remarks, which was communicated to him, and from whence the 

 result is derived, that the nature of the bed of the river has the 

 same influence on the phenomena of congelation in small and in 

 large currents of water. In the Vosges, a superintendant of 

 forges, informed him, that, to prevent the formation of ice at 

 the bottom of the rivulet which supplied his establishment, he 



