PROCEEDINGS OF THE POLYTECHNIC ASSOCIATION. 381 



temperature of the water was immediately raised to 32 deg., 

 just enough water freezing to evolve latent heat sufficient to 

 bring the temperature of the whole up to 32 deg. 



The Chairman cited the fact that ice will be liquified under 

 pressure, even below 32 deg., as explaining the movement of the 

 glaciers along the valleys of Switzerland. It had been found that 

 these glaciers move from 2^ to 500 feet per annum, horizontally, 

 from the more confined towards the wider mouths of the valleys. 

 It was found, upon setting down a line of stalks directly across 

 the valley, that in a few days the line would be curved, the cen- 

 tral portion moving the most rapidly. Mr. Thompson discovered, 

 in his laboratory, that pressure applied to ice, without any change 

 of temperature, would dissolve a portion of it, which would 

 immediately become solid upon the removal of the pressure.. He 

 took a bar of ice, and by the application of pressure bent it into 

 the form of a hoop, still of solid ice. 



Dr. Vanderweyde stated that a heavy block of stone, lying 

 upon ice, with the temperature below the freezing point, will, by 

 its \veight, melt the ice below it so as gradually to make its way 

 into the ice. 



Dr. Stevens. — Glaciers were found to move ftister by day than 

 by night, and faster in the summer than in the winter season. 

 They never thaw; but there is an expansion of the ice by heat. 

 I do not understand that there is a pressure from the mountain 

 side in towards the middle. 



Dr. Vanderweyde. — In my opinion there is a pressure of the ice 

 upon the ground where it is lying. There is a slight quantity of 

 ice melted, and as the ice field is inclined, there is a slight motion 

 of it. Notwithstanding the valley becomes narrower, the motion 

 will be down the valley, and the ice will conform to the shape of 

 the valley. As the ice presses against an immovable rock the ice 

 will be thawed in front of it, and frozen again behind it, where 

 the pressure is removed, and thus the body of ice is permitted to 

 move. 



Mr. Fisher. — All bodies radiate heat, and also receive heat 

 from other bodies. Heat is passing up through the earth con- 

 tinually, and through the ice ; but anything laid upon the ice 

 has the effect of clothing it and retaining the heat. That I 

 should consider a more plausible explanation than the mere pres- 

 sure of so light a substance. 



The Chairman stated that on the next evening he would be 



