290 Effects of Tetrestrial Radiation. 



soil, at an angle, for example, of 45°, A sandy soil absorbs 

 heat, and continues heated, because sand is an indifferent 

 radiator, and is, moreover, a non-conductor of caloric (heat) ; 

 so that vines, &c., in contact with such a surface, would be 

 more than compensated for the temperature they would lose 

 through the medium of radiation; which would also be at- 

 tenuated from the inclination of the plane. 



At St. Mary's Isle, the seat of Earl Selkirk, near Kirk- 

 cudbright, I remember to have seen a beautiful illustration 

 of my views, in the case of pear trees pinioned to trellis- 

 work on such an inclined surface as I have described ; and I 

 have always understood that the crops of fruit which these 

 trees carried were remarkable both for quantity and quality : 

 indeed, it must be apparent, that, under such conditions, spring 

 frosts can have little or no influence; because these frosts are 

 entirely connected with the principles of radiation, and have 

 little or nothing to do with the temperature of the atmospheric 

 medium. If the soil is not of a sandy consistence, in that 

 case I would employ a thin stratum of sand. I have in my 

 little garden just such a surface inclined and sandy, and have 

 planted vines with an intention to train them on the surface, 

 on a framework, something like cucumbers or melons in the 

 hot-bed. The vine I am making my experiments with is called 

 Miller's black grape. I have already had ample proof that 

 the healthy luxuriance of other tender plants does not suffer, 

 and that frost has little or no effect on such an exposure. 



For the purpose of maturing the fruit, I shall throw a 

 veil of black gauze over the vines ; and this will secure me the 

 effects of a powerful absorption of the calorific rays of the 

 sun's beams. Though the radiation from a black surface is 

 proportional to its absorbent capacity, it will operate during 

 the lengthened day (and at this period of the year the night 

 is reduced. to its minimum) in the maturation of the fruit, 

 while the sandy surface is retentive, from its non-conducting 

 character. If bunches of grapes on vines exposed sub dio, or 

 reared in the open air, be tied up in white bags, they will 

 scarcely ripen, are small, and want flavour; but if other 

 bunches on the same tree be confined in bags of black crape, 

 the contrast is very striking, in the latter being fully ripe, 

 large, and of a flavour equal to those cultivated on a foreign 

 soil. This fact explains the principle on which I would veil 

 my vines with sable weeds ; further explanation would, there- 

 fore, be superfluous and unnecessary. 



Respecting the Chinese method of propagating fruit trees, 

 it is merely requisite to detach a strip, or narrow riband, 

 of bark from the branch or limb which is to be separated. 



