SCIENCE OF COMMON THINGS. 167 



Protection against frost. Cause of fog and mist. 



Because it radiates heat very freely in a bright moon- 

 light night ; in consequence of which it is soon covered 

 with dew, which produces rapid decomposition. 



1O0 O How do moonlight nights conduce to the rapid growth of plants f 



Radiation is carried on very rapidly on bright moon- 

 light nights ; in consequence of which dew is very 

 plentifully deposited on young plants, which conduces 

 much to their growth and vigor. 



1O91 Why is the air in immediate contact with the earth, on a clear 

 night, cooler than tlie air at a little distance from the surface f 



Because it parts with its heat to the earth, which in 

 turn loses it by radiation. 



1O93 How can a thin covering of bass, or even muslin, protect trees 

 from frost ? 



Because any covering prevents the radiation of heat 

 from the tree ; and if trees are not cooled down by radi- 

 ation, the vapor of the air will not fe frozen as it comes 

 in contact with them. 



Bass a kind of matting used by gardeners. 



1093 Why is the bass or canvas itself (which covers the tree) ahvays 

 drenched with deiv ? 



Because it radiates heat both upwards and down- 

 wards j in consequence of which it is so cooled down 

 that it readily chills the vapor of the air into dew. 



1094 What is the cause of mist or earth-fog ? 



If the night has been very calm, the radiation of heat 

 from the earth has been very abundant ; in consequence 

 of which the air (resting on the earth) has been chilled, 

 and its vapor condensed into a thick mist. 



1095 Why does not the mist become devj ? 



Because the chill of the air is so rapid, that vapor is 

 condensedy^site/' than it can be deposited and (covering 

 the earth as a mist) prevents any farther radiation of 

 heat from the earth. 



1096 When the earth can no longer radiate heat upwards, does it con- 

 tinue to condense the vapor of the air ? 



No ; the air (in contact with the earth) becomes about 

 equal in temperature with the surface of the earth itself; 



