206 RADIATION. 



A. 1st Because the awning arrests 

 the radiation of heat from the ground 

 beneath : and 



2ndly It radiates some of its own 

 heat downwards; in consequence of 

 which, the ground beneath an awning is 

 not sufficiently cooled down to chill the 

 vapour of air into dew. 



Q. How can a thin covering of BASS or even 

 MUSLIN protect trees from FROST ? 



A. Because any covering prevents 

 the radiation of heat from the tree ; and 

 if the tree be not cooled down by radiation, 

 the vapour of the air will not be frozen 

 as it comes in contact with it. 



Q. Why is the BASS or CANVASS itself (which 

 covers the tree) always DRENCHED with DEW ? 



A. The bass or canvass covering 

 radiates heat both upwards and down- 

 wards ; and is, therefore, so cooled down, 

 that it readily chills all the vapour of the 

 air (which passes over it) into dew. 



Q. Why does SNOW at the foot of a HEDGE 

 or WALL melt sooner, than in an open field ? 



A. Because the hedge or wall radiates 

 heat into the snow beneath, which melts it. 



