VENTILATION. 



279 



balance-weight e ; an index, /, shows the 

 elevation and depression of the float. 

 When the temperature of the house is 

 increased, the air in the cylinder will 

 immediately expand, and, pressing upon 

 the water in the bottom, will elevate that 

 which is in the tube, and with it, of course, 

 the float will be elevated. The movement 

 of the wheel d, whose axis runs through 

 the valve g, immediately opens the valve 

 in proportion to the extent of the revolu- 

 tion. The heated air which collects in 

 the perforated air-tube h is thus suffered 

 to escape. The length and shape of these 

 tubes may be varied according to circum- 

 stances. If the communication with the 

 external air is to be made at the top of 

 the house, it will be necessary to put a 

 conical cap on the top of the air-tube i, 

 acting upon a spindle so as to turn with 

 the changes of the wind ; and if the com- 

 munication is to be made through the 

 end of the house, a transverse tube will 

 be necessary. A drain-cock, h, is inserted 

 in the bottom of the cylinder, in order 

 that the water may be drawn out and 

 replaced if air should get in by the 

 machine being shaken." 



The celebrated Dr Anderson, the 

 inventor of the patent hothouse, &c, 

 and J. Williams, Esq., " made use of 

 oblong bladders, made fast at one end, 

 and with the other attached by means 

 of a cord to a movable pane or small 

 sash. The bladder being filled with air 

 at the common temperature allowed for 

 the house, and hermetically sealed, the 

 window remains at rest ; but as the air 

 of the house becomes heated, so does 

 that of the bladder, which consequently 

 swells, and assumes the globular form ;■ — 

 its peripheries are brought nearer toge- 

 ther, and, of course, the sash or pane is 

 pulled inwards. In a small house this 

 scheme may answer perfectly well for 

 the prevention of extreme heat. Another 

 mode is by using a rod of metal, such as 

 lead, of the whole length of the house ; 

 and, one end being fixed to the wall, on 

 the other is attached a series of multiply- 

 ing wheels, the last of which works into 

 one, which in various ways may open 

 valves or sashes. As the expansion of 

 lead is considerable, the effect of twenty 

 degrees of increase, with proper ma- 

 chinery, might perhaps guard against 

 extremes, as in the other case. A column 



Fig. 365. 



of mercury, with a piston-rod and machi- 

 nery attached, has also been used, and a 

 ring on a barometrical principle is suggest- 

 ed by Sylvester." — Ency. ofGard., p. 604. 



Deacon's Eolian machine, Dr Reid's 

 chimney, Dr Ure's fan, and various other 

 contrivances, have been suggested for 

 performing self-acting ventilation. How- 

 ever creditable to the inventors, these 

 machines have not been found to work 

 satisfactorily in practice. Probably the 

 great nicety required in their manufac- 

 ture renders them liable to accidents 

 through the carelessness of operatives; 

 or the damp and heat they are subjected 

 to may prevent them from working freely. 



We shall now proceed to record the va- 

 rious modes of ventilation which we deem 

 worthy of especial notice, without regard 

 to their priority of invention. We find 

 the following mode described, with an 

 illustration, in the "Gardeners' Magazine," 

 vol. ii. p. 369, and exemplified in the 

 conservatory of Mr Latour at Craven 

 Hill : " It is on the 

 principle of a self- 

 balanced chandelier. 

 A cord from each sa&h 

 passes over a pully «, 

 fig. 365, and is joined 

 under the stage c, 

 where a weight, b, is 

 attached to them by 

 another pulley, and 

 may either be limit- 

 ed in its descent by 

 the ground, or by 

 the length of the line. 

 By this arrangement, 

 easily understood, either or both sashes 

 may be opened to any extent by a very 

 slight motion of the line, and without the 

 least derangement to the plants, or un- 

 sightly fastenings of the cord." 



The Messrs Booth of Hamburg em- 

 ploy a similar mode of ventilating span- 

 roofed houses in their extensive establish- 

 ment, but carry down the chains and 

 weights within tubular metallic columns, 

 intended to support the ridge of the roof. 



In such cases, flexible copper chains 

 should be substituted for cords, as they 

 are less liable to decay. By such chains 

 the roof of the large circular conservatory 

 at Dalkeith is ventilated, an ornamental 

 column rising in the centre, enclosing 

 the chimney, round which balance- 



