By John Frederic Daniell, Esq. 11 



it slowly subsides, and settles upon every thing within its 

 range. 



The formation of dew is one of the circumstances which 

 modify and check the refrigerating effect of radiation ; for, as 

 the vapour is condensed, it gives out the latent heat with 

 which it was combined in its elastic form, and thus, no doubt, 

 prevents an excess of depression which might in many cases 

 prove injurious to vegetation. A compensating arrangement 

 is thus established, which, while it produces all the advan- 

 tages of this gentle effusion of moisture, guards against the 

 injurious concentration of the cause by which it is produced. 



The effects of radiation come under the consideration of 

 the Horticulturist in two points of view : the first regards the 

 primary influence upon vegetables, exposed to it ; the second 

 the modifications produced by it upon the atmosphere of 

 particular situations.. To vegetables growing in the climates, 

 for which they were originally designed by nature, there can 

 be no doubt that the action of radiation is particularly be- 

 neficial, from the deposition of moisture which it determines 

 upon their foliage : but to tender plants artificially trained 

 to resist the rigours of an unnatural situation, this extra 

 degree of cold may prove highly prejudicial. It also appears 

 probable, from observation, that the intensity of this action 

 increases with the distance from the equator to the poles ; 

 as the lowest depression of the thermometer which has been 

 registered between the tropics, from this cause, is 12°, whereas 

 in the latitude of London, it not unfrequently amounts to 

 17°. But however this may be, it is certain that vegetation 

 in this country is liable to be affected at night from the in- 

 fluence of radiation, by a temperature below the freezing 



