PRO TECTION OF VEGETA TION FROM COLD. 3 



water really does exercise any influence in check- 

 ing, by its absorption, the loss of heat by radiation 

 from the earth's surface, it is, even in the most 

 humid conditions of optically clear atmosphere, 

 insufficient to prevent heavy dews by radiation 

 into space of the latent heat of the vapour from 

 which they are condensed. The quantity of heat 

 thus radiated into space through the clear moist 

 air close to the ground is so great that if instead 

 of being taken from the vapour it were taken 

 from the blades of grass, or other finer parts of 

 plants, it would leave them destroyed by frost. 



In point of fact heat actually is radiated away 

 into very high terrestrial atmosphere and distant 

 interstellar air or aether, from the upper and 

 finer parts of living plants, in so great amount 

 every clear night of summer, that destruction 

 by frost could not be delayed for many hours 

 after sunset without a compensating supply of 

 heat from some extraneous source. This source, 

 on windy nights, is the thermal capacity of 

 the air whirled about, up and down, and among 

 the stems and leaves of the plants. On still 



B 2 



