226 THE PEACH AKD KEOTAEINE. 



atmosphere, and thus a superior wall temperature was generally main- 

 tained throughout the longest nights 



But slightly heated, covered with the thinnest screen of oanras, or 

 eyen uncovered, flued or heated walls were generally able to conserve 

 and diffuse sufficient heat so as to preserve pea'oh and nectarine blossoms 

 from destruction. 



But if the primary object of protection is the conservation of the heat 

 of the wall, it follows that glass is but a weak protector at the best. Of 

 course, when glass is so closely fitted to the wall as to inclose and retain 

 Hi considerable amount of heated air, that air baffles, and for a consider- 

 able time resists, the mass of the atmosphere and the open sky outside to 

 establish an equilibrium of temperature between the trees and surround- 

 ing objects. But as clear glass offers little resistance to the radiation of 

 heat, the heat of the wall and of the inclosed air ultimately, and that 

 within a comparatively short period, sink to the equilibrium of the general 

 mass of air. 



But most glass walls are veils, or top screens, rather than close cases. 

 They seem constructed on the principle of keeping cold out rather than of 

 keeping heat in. The fact is, they can do neither to much purpose. The 

 heat of the wall impinging against glass passes right through it. Sup- 

 posing cold as the opposite of heat for a moment, the cold of the sky, 

 ladiating against a glass coping or screen, passes right through it. 

 A compound process, equivalent to burning the candle at both ends, is 

 thus at work on the heat stored in the wall, the trees, and the soil. 

 And it is little wonder that the result is the tree blossoms are blackened 

 and killed by the frost, notwithstanding the glass protectors. A coat- 

 ing of common whiting, slightly darkened into a grey colour with a dash 

 of soot or other colouring matter, doubles, trebles, or more, the protec- 

 tive power of glass screens or copings, while a screen of bunting canvas 

 or an opaque mat over the glass acts like a cloud spread athwart the sky 

 on a clear frosty night, and completely checks the radiation of heat from 

 the trees and the walls, and protects them so efficiently as to save the 

 crop from being destroyed under all ordinary circumstances. 



Before proceeding to other means of protection, it may be useful to 

 advert briefly to means that are seldom employed, and that are very 

 effective against strong winds in the spring.' These consist in building 

 serpentine walls, with easy curves, instead of straight walls. There is 

 a great saving of material, as a 9in. wall on the curve is as strong as a 

 14in., 18in., or 21in. on the straight. They are also more beautiful, especi- 

 ally for small gardens. The curves may be equal, or the southern recess, 

 for peaches, may be double the size of the convex curve on the same side, 

 which may be clothed with pears. Alternate curves of 10ft. and 5ft. 



