60 BOARD OF AGRICULTURE. 



a wide reputation as a meteorologist, suggests that droughts 

 may be caused by the irregular burning of fallows or large 

 tracts of wood or prairie land in summer, and that man, by his 

 ignorance, may be the cause of them. " The summer rains at 

 present are local, and of very limited extent ; and though they 

 travel towards the east, like winter storms, they are not ex- 

 tensive enough to cover the whole country in their progress ; 

 hence, portions of the country are liable to be parched with 

 drought and hot weather. May it not be possible that this 

 irregularity is in part produced by the irregular burning of fal- 

 lows and prairies, thus producing partial and irregular rains, 

 interrupting the wide-extended and general rains which would 

 otherwise take place as they do in winter ? " 



It is well known that the clouds which produce rain are com- 

 posed of vapor, created by an evaporation from the surface of 

 the earth, and from water, which takes place while the sun 

 shines by day, and is, for the most part, suspended when the 

 dew falls by night. 



This vapor remains in the air until it is condensed into water 

 by a low temperature of the atmosphere, and then ordinarily 

 falls in rain. After it has thus fallen, the whole process of 

 evaporation or creation of vapor, formation of clouds, and con- 

 densation of the vapor into water, must be again gone through 

 with before there can be more rain. This, in summer, gener- 

 ally requires some time ; hence, immediately after a rain in 

 any given place, the air in that region is not likely to be in 

 such a state as is favorable to the production of rain. 



The winds greatly hasten the process of evaporation, while 

 the clouds and the absence of the sun hinder or stop it alto- 

 gether. An increase of temperature, also, usually causes a 

 great increase of evaporation from the surface of the earth. 

 In the proverbially moist climate of England, where the 

 amount of evaporation must be far less than in our own, it is 

 sometimes equal to six inches a month; that is, to an amount 

 of vapor which, if condensed into water, would make six inches. 

 In our climate, of course, it must be much greater. 



If, now, from some local cause, there is a shower of rain, 

 the moisture of the atmosphere, being collected and condensed, 

 moves on in the form of clouds till these clouds no longer find 



