MOISTURE AND DEYXESS. 241 



the temperate zones it amounts to about thirty-seven 

 inches a year, while in the tropics it rises to from 

 ninety to one hundred inches, and that the atmosphere 

 when at the freezing point contains about a two-hun- 

 dredth part of its weight of water, while at 52 it con- 

 tains a hundredth part, or twice as much ; at 74, a fif- 

 tieth part, or four times as much, and at 98, a twenty- 

 fifth part, or eight times as much, and so on in that 

 ratio. 



Now, although the mean annual temperature of the 

 two countries is about the same, it being near London 

 about 48 5', and at Boston 48 9', yet the tempera- 

 ture of the growing months of the two countries pre- 

 sents a marked difference, the mean temperature of 

 every one being with us much higher. But the climate 

 of England is proverbially moist, notwithstanding that 

 the mean annual fall of rain near London is only little 

 over twenty-five inches, while the quantity which falls 

 at Boston is over forty-two inches ; at Charleston, S. 

 C., over forty-five inches ; at Savannah, in Georgia, 

 over fifty-three inches, and at Mobile, Alabama, over 

 sixty inches. 



The amount of sensible moisture of the atmosphere 

 is greater in England than here, though the actual 

 amount existing in our atmosphere must exceed that of 

 the atmosphere even in the eastern part of England. 

 Our soil is consequently drier, and unless we have 

 frequent rains vegetation suffers sooner, and the growth 

 of grass is liable to be checked for the want of moist- 

 ure, and this actually happens more or less nearly every 

 year. 



It is plain that the differences in climate that influ- 

 ence and control the growth of the grasses are chiefly 

 moisture and dryness. Moisture must exist either in 

 the soil or the atmosphere. It is also clear that a lux 

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