ALL FROST PROTECTION METHODS, from the 

 -L\. simplest to the most complicated, can be car- 

 ried on more successfully if the processes by which 

 the earth's surface cools at night and the factors 

 which influence the rate of cooling are well under- 

 stood. 



In the first part of this bulletin an attempt has 

 been made to describe in a simple, elementary man- 

 ner the changes that take place at and near the 

 earth's surface on a frosty night, so that persons 

 protecting plants or trees may be able to understand 

 how their protective devices operate to prevent dam- 

 age and in what manner they are most efficient. In 

 treating a matter of this kind it is practically impos- 

 sible to eliminate all technical terms, but so far as 

 possible these have been carefully explained in 

 simple language. 



The larger portion is given over to a discussion of 

 the various methods and devices now being used for 

 protection against frost, together with a chapter on 

 temperatures injurious to plants, blossoms, and fruit. 



Contribution from the Weather Bureau 



C. F. MARVIN, Chief 

 Washington, D. C. April, 1920 



