MOISTURE OF THE AIR. 185 



wHch is certainly not surpassed by an African harmattan," but 

 one which produces less disastrous consequences, because it is 

 accompanied by a far lower temperature and a weaker solar 

 radiation. The mean degree of moisture of the air near 

 Xondon has been found by Mr. Thompson to be "897, on an 

 average of ten years, while the mean temperature is 50'63 :* 

 in other parts of the world it is very different ; and the amount 

 of those differences, together' with the means of imitating them 

 artificially, constitutes one of the most delicate and difficult 

 parts of the gardener's art. All that relates to this subject, 

 however, to be treated usefully, must be considered in a very 

 special way, and in such detail as can only be expected in a 

 separate work upon the subject. An idea of the difference 

 between the atmospherical moisture of London and that of 

 other parts of the world may, however, be collected from the 

 following table showing the amount of rain that falls in a few 

 different countries. 



Incites per annum. 



London 24'01 Average of 10 years. 



St. Petersburg ... IB- 

 Algiers 27* 



Fattehpiir (East Indies) 35*94 Average of 4 years. 



Madeira 31- 



Sagar (East Indies) . . 31-15 to 64-76 

 SikHm, at 11,000 feet . 40- 



Bahamas 54-99 



Calcutta 59-83 to 81- 



Ceylon 84-3 



Macao 48-8 to 107-3 



Equator 96- 



Dorjiling 122-26 



Coast of Malabar . . . 123-50 Average of 14 years. 



Grenada. ..... 126- 



Leogane, St. Domingo . 150- 



Bengal 20 to 22 inches in a single month. 



Bombay 32 inches in 12 i 



™, f 203-5 inches in six months ; as much as 8-5 



^^"^ I in a day (July 31, 1831). 



• See the various meteorological journals putlisied by the Horticultural Society, 

 in their Transactions, from the year 1826 inolusi-^e. 



