288 



VENTILATION. 



rollers. They are kept in their place when 

 shut, or at any point of ventilation, by a 

 spring catch fixed to the side of the rafter. 



One great objection to ventilation 

 being effected by sliding one sash down 

 over the other is, that there is a double 

 portion of glass over a considerable 

 part of the roof— therefore a double 

 portion of light must be excluded : as 

 light so transmitted will be doubly de- 

 composed by passing through two sur- 

 faces of glass, a considerable loss of light 

 must ensue. But the greatest objection 

 of all is the breakage of glass. 



In the Royal Gardens at Frogmore a 

 very efficient and simple mode of ventila- 

 tion is adopted ; and we believe the 

 merit of its construction is due to Mr 

 Jones, the eminent hothouse builder of 

 Birmingham, who executed the whole of 

 the extensive range there. Front ventila- 

 tion is effected by the whole of the upright 

 lights being opened simultaneously, either 

 to their whole extent, or otherwise. These 

 lights are provided each with a brass 

 pinion, fixed to their centre, and working 

 into a toothed quadrant, which is attached 



Fig. 387. 



Fig. 385. 



to an iron shaft ex- 

 tending the whole 

 length of each house. 

 This shaft being turned 

 round by means of a 

 handle at one end, the 

 quadrants are either 

 thrown out or drawn 

 in, according as the 

 handle is moved back- 

 wards or forwards, and 

 can be kept in any 

 position required. — Vide fig. 385. 



The ventilation at the top of the back 

 wall is effected by having openings, from 

 3 to 4 feet long and 6 

 inches deep, as shown in 

 fig. 386, left under every 

 alternate sash, and open- 

 ing above the roof at a. 

 These upper openings 

 are provided with iron 

 gratings, to prevent birds, 

 &c, from entering the 

 house ; and communi- 

 cate with similar openings within the 

 roof, which are provided with shutters 

 moving on pivots, as shown at b. These 

 are opened or shut simultaneously by 

 turning the screw a, fig. 387, connected by 



Fig. 386. 



the iron rod b to the lever c, which is fixed 

 to the rod of wrought-iron extending the 

 whole length of the roof. 

 To this shaft are fixed 

 the small levers c, one 

 of which is attached by 

 a wrought-iron link to 

 each ventilating door or 

 shutter — so that, by 

 raising or lowering the 

 lever by means of the 

 screw, the shaft is turned 

 more or less round ; 

 and this, acting on the 

 levers, opens and shuts 

 the ventilating doors 

 simultaneously the whole 

 length of the house. The 

 top sashes of the roof of 

 these houses slide down, and this movement 

 is regulated by a semi-circular contrivance 

 of iron, resembling half a cog-wheel, and 

 a catch. A movable handle turns this 

 wheel to any extent, by which means the 

 lights are let down as far as may be 

 requisite, and are there kept stationary. 

 To close them it is requisite only to reverse 

 the operation. 



The previous remarks on ventilation 

 have reference for the most part to lean-to 

 houses — that is, glass structures built 

 against a wall. Houses on the curvilinear 

 and span-roofed principle are ventilated 

 at top somewhat differently. Ridge-and- 

 furrow roofs may be ventilated at top, by 

 having the ends of each bay made so that 

 they can be opened to their full extent. — ■ 

 Vide Ridge-and-Fukrow Pit. The poly- 

 prosopic roof — which is a species of cur- 

 vilinear roof — admits of the greatest faci- 

 lity in ventilation, being composed of 

 many faces, hinged at their upper angles. 

 Rods being connected with the lower 

 "outside corners of these faces, and ter- 

 minating in chains which go over pulleys 

 in the top or above the back wall, the 

 whole roof, including the ends, may be 

 opened or raised simultaneously, like 

 Venetian blinds, either so as each sash 

 or face may be placed in the plane of the 

 angle of the sun's rays at the time, or to 

 the perpendicular, to admit a shower of 

 rain. In consequence of this arrange- 

 ment, the plants in a polyprosopic house 

 may, at any time, and in a few minutes, 

 be placed in effect, or as far as respects 

 light, air, wind, rain, dew, &c, in the 



