4 



On Climate, fyc. 



Horticulturist is to stretch, as it were, his climate to the 

 south, where these extremes of drought and cold never 

 occur ; and not only to guard against the injurious effects of 

 the ultimate severity of weather, but to ward off the sudden 

 changes which are liable to recur in the different seasons of 

 the year. To enable us to understand the methods of effecting 

 this end, it will be necessary to consider the means by which 

 these changes are brought about in the general course of 

 nature. The principal of these will be found to be, wind 

 and radiation. 



The amount of evaporation from the soil, and of exhala- 

 tion from the foliage of the vegetable kingdom, depends upon 

 two circumstances, the saturation of the air with moisture, 

 and the velocity of its motion. They are in inverse propor- 

 tion to the former and in direct proportion to the latter. 



When the air is dry, vapour ascends in it with great rapidity 

 from every surface capable of affording it, and the energy of 

 this action is greatly promoted by wind, which removes it 

 from the exhaling body as fast as it is formed, and pre- 

 vents that accumulation which would otherwise arrest the 

 process. 



Over the state of saturation, the Horticulturist has little 

 or no control in the open air, but over its velocity he has 

 some command. He can break the force of the blast by 

 artificial means, such as walls, palings, hedges, or other 

 screens ; or he may find natural shelter in situations upon 

 the acclivities' of hills. Excessive exhalation is very injurious 



calculation, and more detailed explanations than it is possible to comprise in a 

 note, may be had, with the hygrometer, at Mr. Newman's in Lisle Street, or may 

 be found in the author's Meteorological Essays. 



