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Strange as it may appear, yet it is nevertheless 

 true, that a screen is more beneficial in preserving 

 the temperature of trees, when from three to six 

 inches from them, than when in immediate contact 

 with their surfaces. When a woollen net was sus- 

 pended four inches from the wall on which a peach 

 tree was trained, the thermometer fell very slowly, 

 and the lowest degree it reached was 38 degs. ; when 

 the same screen was twelve inches off, it fell to 

 34 degs. ; and when drawn tightly over the tree, it 

 barely kept above 32 degs., the temperature of the 

 exterior air. When at twelve inches from the wall, it 

 permitted the too free circulation of the air; and 

 when in immediate contact with the polished bark of 

 the peach, perhaps another law of cooling came into 

 operation. The law is, that polished surfaces radiate 

 heat slowest. Thus, if two glass bottles, equal in 

 size and thickness of glass, and of the same shape, be 

 filled with warm water, and one of the bottles be co- 

 vered with an envelope of fine muslin, this bottle will 

 give out heat to the surrounding air with much 

 greater rapidity than the other bottle ; so that, in a 

 given time, the bottle with the envelop will be found 

 colder than the one which has no covering. 



Screens, such as the preceding, or the slightest 

 agents, sprays of evergreens, placed before the 

 branches of wall-trees or other plants, as already no- 

 ticed, operate beneficially in another way, checking 

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