46 AGRICULTURAL TEXT-BOOK. 



amount of rain that falls in a year is governed by known laws. 

 It varies in different parts of the same country, but is nearly the 

 same, each year, in any given locality. 



Rain is measured, for meteorological purposes, by inches. The instru 

 ment used is called a Rain Guage, anu sometimes a Pluviometer. They 

 are of various forms, but all acting upon the same principle that of re 

 ceiving the rain into a vessel of known size, with a graduated measurer, 

 divided into inches and parts of inches. The one generally used in the 

 United States is known as the &quot; Conical Rain Guage of DeWitt&quot; 

 equally simple and perfect. It consists of a copper cone, with a perfora 

 ted cap to prevent evaporation. It is fixed on a post, in a situation 

 sheltered from winds, about 8 feet from the ground. The measurement 

 is made by putting down perpendicularly to the bottom of the guage, a 

 measuring stick, graduated in inches and their decimals. 



136. In Agriculture, rain is important as regards (a,) the 

 season, and (b,) the mode in which it falls, whether in heavy 

 storms, with long intervals between them, or frequently, in small 

 quantities at a time ; and (c,) the direction from which it comes. 

 If rain chiefly fell late in the Fall, in Winter, or in early Spring, 

 vegetation would receive but little benefit from it. If it fell 

 continuously at seed and harvest time, it would preclude cultiva 

 tion ; if it fell in heavy storms, with long intervals between them, 

 plants would be alternately forced forwards, and retarded. 

 Where rain is very constant, as in the mountains of E no-land 

 and Scotland, grass-growing and cattle-raising are substituted for 

 grain. Consequently, the annual amount of rain is of less im 

 portance than the frequency of it, and the seasons of the year 

 over which it is spread. 



The annual amount of rains, averages : 



Under the tropics of the New World, 115 inches. 



&quot; &quot; &quot; &quot; &quot; Old World, - - Y6 

 Within the tropics generally, - 95j &quot; 



In the United States, - 45 &quot; 



Europe, - 3 If &quot; 



Generally over the world, - ... 34 J 



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