72 ROYAL SOCIETY OF CANADA 



because everyone neglects what his predecessor neglected, and because 

 academical collections, in which many treasures remain concealed, are 

 very seldom consulted. 



In 1730, at an atmospherical temperature of — 9° centigr. (15°. 8 

 Fahr.), Hales saw at Teddington, the surface of the Thames, near 

 the banks, covered with a layer of ice one-third of an inch in thickness. 

 There was also at the same time a second layer below, of greater 

 thickness^ which followed the depth of the river, as it adhered to the 

 bottom. This sheet was united to the upper one even on the water- 

 side; but it was gradually separated in proportion, as, in proceeding 

 into the river, the 'depth of water increased. It was not so solid as 

 the first, and was mixed with sand, and even stones, which the flakes 

 sometimes carry with them in their movement upwards. 



This observation is defective, inasmuch as it was made too near 

 the bank. Those who do not know how imperfectly every kind of 

 soil transmits heat, might suppose that the cold was communicated 

 from the dry ground of the bank to that which formed the bed of the 

 river by means of conductibility. , It is unnecessary to discuss this 

 difficult point, as it has no connexion with many of the cases which 

 are about to occupy our attention. 



It is really surprising that those ^vriters who have lately con- 

 sidered the subject of floating ice in a historical point of view, have 

 not alluded to some observations which were made in France a good 

 many years ago. 



At the close of December, 1780, the temperature was very suddenly 

 decreased in the southern parts of France by a very strong northerly 

 wind. The thermometer sunk to 8° or 7° centigr. below zero. 

 Besmarest, member of the Académie des Sciences, who, at that time, 

 happened to be at Annonay, saw the bed of the Dèome covered with 

 ppongy ice. The frost commenced at first on the margin of the river, 

 where there was a depth of water to the extent of two or three feet. 

 The cold continuing, the ice soon shewed itself in the deepest parts. 



In places where the water flowed over the tare rocks, Desmarest 

 saw no vestige of ice. On the contrary, it was rapidly formed in 

 great abundance, especially where there was any quantity of gravel; 

 in some parts it was two feet thick. 



According to Desmarest, " it was from the lower part which 

 touched the bottom, that the flakes of ice successively increased . . . 

 The ice already formed was continually raised up by the expansive 

 force of that which was in the act of formation .... In watch- 

 ing its motion, I have seen," said he, "that certain flakes of the ice 

 were raised up five or six inches in a single night. Some of them 



