348 Prof. Tyndall on some Physical Pi-operties of Ice. 



Mr. Harrison, who had devised and perfected a machine for the 

 manufacture of ice by the evaporation of sether. I first examined 

 a mass of ice of the shape of the frustum of a cone. The 

 diameter of the base was lOh inches, of the top 7\ inches, and 

 the length of the frustum was 2 feet. During the freezing of 

 this mass a thermometer fixed on the ice showed a temperature 

 of 8° below the zero of F., or 40° of F. below the freezing-point 

 of water. 



45. Fourteen hours after it had been frozen, the temperature 

 of the mass, to a depth of 2 inches below the surface, was accu- 

 rately 32° F. At the heart of the frustum the temperature was 

 31^°. The superficial portions of the frustum had been the cold- 

 est, and we see that in fourteen hours the ice of these portions 

 rose forty degrees in temperature. 



46. On the 24th of April, Mr. Harrison had the kindness to 

 place his excellent machine entirely at my disposition. The 

 vessel which contained the water to be frozen was shaped like 

 the inverted frustum of a cone, and was surrounded by a jacket, 

 between which and the side of the frustum vaporized aether cir- 

 culated, the whole being placed in a vessel of water. At 11 

 o'clock A.M., I placed a thermometer (A) in contact with the side 

 of the vessel, and about 2 inches below the surface of the water. 

 The machine commenced to act, an opalescence was soon obser- 

 vable on the sides, and after twenty minutes' action the thermo- 

 meter was firmly imbedded in the ice. At 1 o'clock p.m., a 

 second thermometer (B), placed at a distance of an inch from 

 the side of the frustum, was also surrounded by ice. At 2^ 20"" 

 P.M. a third thermometer (C) was placed at a distance of 1 finch 

 from the side of the vessel, and at b^ 30"* p.m. a fourth thermo- 

 meter (D) was placed at a distance of 3 inches from the side. 

 The observed temperatures of these thermometers at the times 

 stated are given in the following Table : — 



At 8'> 30" P.M. the machine was stopped and the supply of 

 Hither was cut oflP. Tlic mercurial columns began to rise gra- 



