VENTILATION. 



289 



open air; and being so placed, may, 

 whenever desired, be as speedily restored 

 again to their former climate." — Ency. of 

 Gard. p. 585. All curvilinear roofs are 

 difficult to ventilate, the safest plan being 

 to let the sashes slide down over each 

 other in Niven's manner, elsewhere no- 

 ticed. But the most efficient is to hinge 

 the sashes at their upper angles, and cause 

 them to open outwards by means of iron 

 levers at their lower 

 Fl - yys extremities, fig. 388, 



where such ar- 

 rangement would 

 not interrupt the 

 plants growingwith- 

 in, such,forinstance, 

 as vines or peaches 

 trained near to the 

 glass. The whole 

 sides and roof of metallic houses in particu- 

 lar may be made to open upon the poly- 

 prosopic principle ; but instead of hingeing 

 them at the top of the opening parts, these 

 parts may be hung on pivots at their cen- 

 tres, one-half opening outwards, and the 

 other inwards — the casements being half- 

 checked into each other, so as to overlap 

 when closed, for the exclusion of rain. 

 The difficulty which presents itself in ob- 

 taining sufficient ventilation, is one of the 

 greatest objections to this form of roof. 



Span-roofed houses are now becoming 

 popular — and very justly, as they combine 

 many of the perfections, and few of the 

 imperfections, of all other kinds of glass 

 structures. We have shown (fig. 366) one 

 mode of top-ventilating such houses, and 

 will instance a plan adopted by ourselves. 

 The ridge, instead of being composed of one 

 thick beam of 

 timber, is formed 

 of two 2-inch 

 planks, a a, fig. 

 389, 9 inches 

 broad, and ex- 

 tending the 

 whole length of 

 the roof. These 

 are kept apart 

 to any required 

 distance — say 

 from 3 inches to 

 1 foot, or more, 

 according to the 

 amount of ven- 

 tilation desired. Fig. 389 is a section of the 



VOL. I. 



ridge when fully open ; fig. 390, a longitu- 

 dinal view when nearly fully open ; and fig. 

 391, of the same when shut. The planks 



Fig. 390. 



a a forming the ridge are kept in their 

 place by iron bolts. The capping b is 



Fig. 391. 



lifted and shut, by being attached by 

 hinges to the tumbler c. This is acted 

 upon by the levers d e. To each of 

 these again is attached a line passing over 

 a pulley in the upright h h, (which also 

 supports the roof.) By pulling the right- 

 hand line in fig. 391, the lever d is drawn 

 towards the perpendicular, more or less 

 according to the amount of ventilation 

 required, and kept at the desired point by 

 fastening the line to a stud in the upright. 

 The levers, d e, as well as all the tumblers, 

 c in fig. 389, are acted upon at the same 

 instant. By pulling the left-hand line, the 

 whole action is reversed, and the capping 

 or top of the ridge b falls close down, and 

 ventilation is suspended. A house 60 or 80 

 feet long may be ventilated by this means ; 

 but, of course, if the house is longer, it 

 will be better to divide the ventilation 

 into two pieces. Back and front air may 

 be given to lean-to houses on the same 

 principle, it requiring but a very slight 

 modification to adapt it to such circum- 

 stances. The houses ventilated upon this 

 principle have fixed roofs, glazed with 

 sheet-glass 9 inches by 21, and nearly 

 air-tight. Front ventilation is obtained 

 in one case by means of openings in the 



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