Prof. Tyndall on some Physical Properties of Ice. 349 

 dually, and at 10 o'clock p.m. they were found to be as follows : — 



A. B. C. D. 



27° 27° 271° 28|° 



The machine rested throughout the night, and at 8 o'clock on 

 the morning of the 25th all the thermometers stood at 32°. 



47. The machine was set going at 8 a.m. on the 25th, and 

 continued working until 2 o'clock in the afternoon, its office 

 now being, not to freeze, but to cool the ice already frozen. The 

 thei'mometers were read off every quarter of an hour, but it is 

 not necessary to record all the observations. The following are 

 the temperatures noted at 8 and ll'^ 30"" a.m. and at 2 p.m. : — 



48. At 2^ 45™ the machine was stopped and the supply of 

 {ether cut off. The upper surface of the ice was covered with 

 2 inches of hair-felt : the water surrounding the frustum and its 

 jacket was at a temperature of 32°; the thermometers were read 

 off every half-hour, but I will limit myself at present to a few 

 observations. The temperatures at 2 o'clock were those stated 

 at the close of the last Table. 



Time of observation, A. B. C. D. 



On the 26th the following temperatures were observed : — 

 A. B. C. D. 



At 1'' 30"" a hole was bored in the centre of the frustum to a 

 depth of 5 inches, and in this another thermometer (£) was 

 placed ; its temperature at 3'' SO-" p.m. was 30|°. At 8 o'clock 

 in the morning of the 27th the observed temperatures were the 

 following : — 



A. B. C. D. E. 



32° 32° 32° 32° 32° 



