112 ON THE POSSIBILITY OF PREVENTING DAMAGES BY FEOST. 



On the basis of what we have pointed out above with regard 

 to the causes of night frosts and their effect on the vegetable 

 world, we get a 



Theory of Frost Prevention 



that ravages by night-frosts can be avoided if we can restore to 

 the field the anaount of heat lost by radiation, or if we can 

 redupe this radiation, or prevent a too rapid thawing of the 

 frozen plants. 



We can effect a communication of heat to the plants in the 

 following way : — 



(a) By a reduction of the radiation by means of artificial 



clouds ; 

 (h) By movements in the air which mix the different strata; 

 (c) By condensed moisture that affords heat. 

 Nature herself offers certain opportunities which are of the 

 greatest importance : — 



(a) The condensation of vapour continually going on during 



the night ; 



(b) The univet-sal calm which is reigning during a frosty 



night. 

 Now we will consider how this theory can be put into prac- 

 tical use, and give a resume of 



The Methods of Frost Prevention. 



From time immemorial it has been known that frost will 

 not occur when the sky is cloudy, and in many lands trials have 

 been made to produce artificial clouds by burning different kinds 

 of more or less cheap combustibles. The ancient Romans used 

 this method as we learn from their literature, and in Peru the 

 old inhabitants used smoke as a preventive against frost long 

 before the country was taken possession of by Europeans. 



No completely successful method has however yet been 

 devised, and smoke as a preventive has therefore got into dis- 

 repute. In France, for instance, the people say it succeeds but 

 always for the advantage of our neighbours, thus indicating that 

 smoke and vapour pass to their neighbours' fields. I have heard 

 the same remarks in Queensland. But neither the French nor 

 the Queenslanders have formed any association, as is the case in 

 many parts of Germany, where attempts have been made to 

 protect vineyards and orchards against both spring and autumn 

 frosts by the burning of coal tar. 



