132 



HOTHOUSE-BUILDING. 



or caps according to taste and circum- 

 stances. In long ranges, this retaining 

 wall may be in a straight line, whatever 

 may be the breadth of the houses, though 

 perhaps it would be better that it should 

 be in breaks corresponding with their 

 respective breadths. In this latter case, 

 however, it will be necessary to have, as 

 is usually the case, the highest and 

 broadest house in the centre. By this 

 plan, also, ample means will be offered for 

 subterranean ventilation, the openings 

 of the air-drains being in the retaining 

 wall, and covered with ornamental re- 

 volving brass ventilators, the air being 

 conducted in tubular earthenware pipes 

 under the borders ; or where these do not 

 exist, as in the case of plant-houses, or 

 where the roots are confined within the 

 walls of the house, as should be the case 

 in wet and cold countries, it is brought 

 under the terrace walk, which should, ac- 

 cording to all principles of good taste, occu- 

 py their place. The air thus admitted can 

 be diffused regularly over the house, and 

 made to ascend from under the pathways, 

 by the sides of the walls near the surface of 

 the floor ; and those disastrous conse- 

 quences may be avoided, which always fol- 

 low the admission of cold air immediately 

 upon the young tender leaves and shoots. 



In regard to magnitude, we believe 

 that hothouses may be carried to any 

 extent of area, provided the height does 

 not exceed certain limits. What these 

 limits are, experience has not as yet 

 taught us ; but that the strength of a 

 structure is diminished as its magnitude 

 is increased, appears to be fully admitted. 

 The following reason ing is given by Dr 

 Lardner in his recently published " Hand- 

 book of Natural Philosophy," &c. — "If 

 any structure be increased in magni- 

 tude," says this authority, "the propor- 

 tions of its dimensions being preserved, 

 the strength will be augmented as the 

 squares of the ratio in which it is increased. 

 Thus, if its dimensions be increased to a 

 twofold proportion, its strength will be 

 increased in a fourfold proportion ; if they 

 be increased in a threefold proportion, its 

 strength will be increased in a ninefold 

 proportion, and so on. But it is to be 

 considered, that by increasing its strength 

 in a twofold proportion, its volume, and 

 consequently its weight, will be increased 

 in an eightfold proportion ; and by in- 



creasing its dimensions in a threefold 

 proportion, its volume and weight will 

 be increased twenty-seven times, and so 

 on. Thus it is apparent that the weight 

 increases in a vastly more rapid propor- 

 tion than the strength, and that, conse- 

 quently, in such increase of dimensions, a 

 limit would speedily be attained at which 

 the weight would become equal to the 

 strength, and beyond this limit the struc- 

 ture would be crushed under its own 

 weight. On the other hand, the more 

 beyond this limit the dimensions of the 

 structure are kept, the greater will be the 

 proportion by which the strength will 

 exceed the weight. All works, natural 

 and artificial, have limits of magnitude, 

 which, while their materials remain the 

 same, cannot be exceeded." 



In regard to economy in construction, 

 and also for houses in which very early 

 and very late crops are to be expected, 

 long narrow houses will be found more 

 satisfactory than those of a very great 

 breadth ; and those with steep roofs more 

 so than those with flat ones, as in both 

 cases much depends on their being placed 

 at such an angle of elevation as will pre- 

 sent these roofs most favourably to the 

 sun's rays when it is low in the horizon, 

 and also because the plants are nearer the 

 glass. On this subject Mr Loudon 

 remarks, "There is another reason in 

 favour of narrow houses, where perfection 

 of growth and economy are objects, which 

 is, that a considerable portion of the heat 

 by which the temperature of hothouses is 

 maintained is supplied by the sun. The 

 power of the sun, therefore, will be great 

 on the atmosphere within inversely as its 

 cubic contents, compared with the super- 

 fical contents of the glass enclosing it. 

 Thus, supposing one house to be 20 feet 

 high and 20 feet wide, and another to be 

 20 feet high and only 10 feet wide, the 

 contents of the former will be exactly 

 double that of the latter; at the same 

 time, instead of containing double the 

 surface of glass on its roof, it will scarcely 

 contain one-third more, being nearly in 

 the proportion of 28 for the house of 

 double volume, to not 14, or one-half, but 

 22, for the one of half the internal capa- 

 city. In the wide house every square 

 foot of glass has to heat upwards of 7 feet 

 of air ; in the narrow house, only about 

 4^ feet." The experience of ages confirms 



