[barxes] temperature RECORD OF NOCTURNAL RADIATION 139 



right took- place and lasted until 9.30, when the plate was removed 

 entirely. The trace for the remainder of the night was for the direct 

 radiation to the sky. I can only account for the radiation through 

 the mica plate after 5.30 as idue to a clearer sky or to a diminution 

 of ahsorption of diffused sunlight as the evening approached. The 

 mica plate was of a light yellow colour. 



In Fig. 15 is shown the radiation through two inches of a clear 

 ice bloclc, which was cut from a large block of clear river ice. At 

 8.30 the wooden cover of thermometer P was opened and the maximum 

 cooling obtained. Between 9 and 10 some ice blocks were tried of 

 different thicknesses and clearness, with varying results. At 9.45 the 

 two inch block was put in place and left over the thermometer for the 



^â/£9 /WarcA '06. 



Fig. 16. Radiation Through 4 Inches Clear Ice, Compared with Radiation 

 Direct. Air Temperature 28° Fahr. 



remainder of the night. It will be seen that the radiation reaches 

 Yen- nearly the maximum attained for the early part of the night. 



In Fig. 16 is shown the effect of placing a block of clear ice four 

 inches thick over the thermometer C, in this case at 7.15 o'clock. The 

 trace from 4.35 to this time being for direct radiation. The ice block 

 cuts the radiation down to about one-half of its previous value, since 

 it was diminishing gradually from 6 to 7 o'clock. 



Owing to the stress of other duties the traces had to be discon- 

 tinued, but it is hoped that further work may be carried out next 

 winter, both on the transparency of various substances for the earth's 

 radiation during some extremely cold, clear weather, and in relation to 

 the cloudiness of the sky. It seems likely that the traces might prove 

 of service in meteorological work in the latter connection. 



