1878.] 



Conductive Properties of Ice. 



185 



meter TY was placed on the inner side of the upright M, having its 

 bulb exposed to the air and 5 inches distant from the lamp. Having 

 found from experiments I and II that a certain amount of radiation 

 really existed, a broad screen, composed of layers of lint and pasteboard, 

 was placed against the outer side of the upright M, and perforated, so 

 as to closely encircle the bar in its passage through. This screen was 

 used in III and subsequent experiments. 



In order to be free from draughts, and yet to be in a place of low 

 and pretty uniform temperature, the observations were made in a 

 closed-in ice-building on the floe (that which was used as a theatre), 

 and the temperatures of the external air and of the air inside the 

 building were on each occasion noted. It was found that whenever 

 the temperature in the open air was below —20° F., the temperature 

 inside the building was about 10° warmer ; this difference being 

 accounted for by the heat conveyed through the floe from the sea-water 

 beneath. 



From a mean of five experiments on fresh- water ice it appears that 

 in one hour from the time when heat was applied, the temperatures at 

 the distances of 6, 10, 14, and 18 inches from the source of heat had 

 risen 4°-45, 1°78, l°-30, and 0°'25, respectively. This result furnishes 

 a rough method of estimating the absolute rate of conduction. It 

 would have been more satisfactory if in all cases the observations 

 could have been continued until the thermometers indicated fixed 

 temperatures, but this was impracticable from the thawing of the end 

 of the ice-bar ; and if but a very moderate heat had been applied, the 

 changes in temperature would have been hardly appreciable. In most 

 cases but little change in temperature took place after the hour had 

 elapsed, and in the case of experiment VIII, when a series of observa- 

 tions extending over two hours was carried out, the thermometer 

 indicated no material change in temperature throughout the second 

 hour. 



Table VI gives the results of a series of observations upon a bar of 

 sea-water ice, the rise in temperature being respectively 4°, 2°, l° - 5, 

 and 1*°5. 



It will be seen that in Tables I, II, and III, the temperatures indi- 

 cated by thermometer YY are given, and that in I and II its ranges of 

 temperatures are respectively 4° and 2°*5. In III the screen to prevent 

 radiation was used, and every precaution was taken that the tempera- 

 ture of the ice-house might be uniform throughout the course of the 

 experiment. In this case thermometer YY shows a rise in first hour 

 of only ,o 25. To exhibit this more clearly Table VIII (the first half 

 of which is only a repetition of Table III) is given, when the results 

 of observations extending over two consecutive hours are recorded ; 

 and from which it appears that the ice thermometers indicated almost 

 fixed temperatures from the end of the first hour. The temperature of 



