250 



The Data on which ice have to depend 



With cold winds the temperature of our inland lakes would 

 be much more quickly cooled than by radiation ; but for the 

 formation of dew it is necessary that there should be scarcely 

 any wind. It is also necessary that the water should abstract 

 heat from the air, and not that the air should abstract heat 

 from the water. 



Dr. Wells also clearly proved by his experiments that 

 water fully exposed in a calm clear night in shallow vessels 

 lost weight from evaporation, while dew was being largely 

 deposited on the surface of the ground. An Increase of 

 weight from condensation of dew was only observed when the 

 cold was so great that ice was formed, and in this case he 

 found a slight increase in weight, but the existence of ice 

 proved that the temperature of the water had been reduced 

 far below the dew point. 



I am not aware that any subsequent experiments have shown 

 any inaccuracy in the experiments of Dr. AVells. 



It is to this uniformity in the temperature of water during 

 day and night that our land and sea breezes are owing. 

 During the day, the air over the land becomes heated, and a 

 sea breeze is the result ; during the night, the land is chilled 

 by radiation, and the air being thus rendered much colder and 

 heavier than that on the surface of the ocean, a land breeze 



is the result. n 



In this manner, the extremes of heat and cold are very 

 much moderated along the coast lines, and the climate is 

 rendered much milder and more agreeable. 



There can be no doubt that like atmospheric currents wdl 

 take place at Yan Yean. The heated surface of the sur- 

 rounding ranges, during the day, will produce currents oi 

 cool air from the reservoir. During the night, the warmer 

 air on the surface of the reservoir will give place to currents 

 of cold air which has been deprived of its moisture by the 

 chilling influence of radiation on the summits and slopes ot 



the ranges. ^ ^ ^ , 



Mr. Hodgkinson's theory, would, however, reverse the 



whole order of things. . i i i i i 



If the surface of the sea and our inland lakes becomes 

 durino^ the night so much colder than the surface of the land 

 as to Condense double the amount of dew, we_ should have 

 land breezes in the day, and sea breezes m the night ; and our 

 summer watering places would become inhospitable deserts. 



But as it is physically impossible for our inland lakes to 

 lose from 5^ to 15^ of temperature by radiation during the 

 night, so it is physically impossible for any dew to be con- 

 densed on their surface. 



