relatively to maintaining a high Temperature. 377 



questionable whether the effect of the increased altitude of the 

 sun at twelve o'clock may not be almost lost on account of the 

 obliquity of the angle. The original purpose of this house was 

 to grow pines and kidneybeans through the depth of winter, 

 and strawberries from March till a supply could be obtained 

 from the open ground. In Jig. 73., the angle of incidence, on 

 December 21., is 41°, which, according to the above table, 

 admits nearly 966 rays ; leaving a sensible balance of transmitted 

 rays in favour of Jig. 73. 



Let us next consider these two houses with regard to their 

 different capacities for retaining and radiating internal heat. 

 Fig. 72. has a metallic roof, and is, therefore, a greater con- 

 ductor of heat and cold than Jig. 73., which is of wood. 

 Fig. 72. has a flat surface, and is, in consequence, much more 

 susceptible of cooling, during the absence of the solar rays, than 

 Jig. 73., which is comparatively steep. Of this consequence any 

 person may convince himself, by placing an object of a cubical 

 form in the open air during a frosty night, with one of its six 

 sides in a horizontal position : the upper horizontal side will be 

 covered with hoar-frost, while the four sides vertically exposed 

 will be comparatively, if not absolutely, exempt from it. The 

 cause is obvious : hot air takes an upward direction, and cold 

 air the contrary, unless when acted on by some powerful 

 horizontal force, . as, for instance, wind. On this principle, 

 therefore, the steeper the surface, the less favourable it becomes 

 to radiation; and the more horizontal, the more favourable. 

 Fig. T2. is wide, and is therefore less easily heated; and, from 

 its construction, it cannot admit of being covered during severe 

 weather. Fig. 73. is narrower, and therefore is more easily 

 heated, and can readily be covered during severe weather ; 

 which gives it an additional advantage over Jig. 72. " Oh ! " 

 but some may say, " only apply a little more fuel, and that ob- 

 viates all your objections." But I say, without hesitation, this 

 can never supply the deficiency ; for the heat that is given out 

 by a smoke-flue, or hot water or steam pipe, as these are com- 

 monly constructed, is not only deprived of its hydrogen, which 

 is so favourable to vegetation, but it is also, in the case of a 

 smoke-flue, so loaded with sulphureous effluvia, that nothing 

 subjected to its influence can thrive ; and many tender plants 

 will actually dwindle away. Each of these houses may be very 

 good in its place : Baldwin's both to grow and fruit pines ; and 

 the other to fill with plants ready to fruit about the middle of Fe- 

 bruary or the beginning of March, to let them remain in until the 

 fruit are all cut, and then to let the house be unemployed till the 

 sun again commences his course towards the northern hemi- 

 sphere. To attempt, however, to grow kidneybeans in such 



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