in the Garden of the Horticultural Society. 381 



is necessarily no upright glass in front of the house ; but the 

 roof rests there upon the solid wall, and at back upon the 

 face of the back wall. In the front wall are built a number 

 of wooden frames, into which shutters opening externally on 

 hinges, are accurately fitted. In the back wall within the 

 house, and next the glass at top, are also fitted a corresponding 

 number of wooden frames furnished with a wooden slider, 

 running up and down by means of pullies with cords and 

 weights, after the manner of a window-sash. These sliders are 

 interposed before a hollow in the wall, which communicates 

 with the external air in front above the glass roof of the 

 house. When it is wished that no air shall be admitted, the 

 front shutters and the back sliders are closed, and in propor- 

 tion as it is desired to ventilate the house, are they opened 

 to a greater or less degree. By these means a current of air 

 is maintained from front to back ; and as fast as the admitted 

 air becomes heated, and rises in the house, it escapes through 

 the ventilators at the top of the back wall. When it is ex- 

 pedient to admit fresh air, without loss of much heat, the 

 front ventilators alone are opened. The ventilation of the 

 houses being thus effected with facility and accuracy, renders 

 the moving the lights for that purpose unnecessary ; and, in 

 consequence, all the sashes in the Houses erected in the Garden 

 of the Society, excepting those of the Peach-house, are now 

 fixed. By aid of these ventilators, the temperature of iron 

 houses is capable of being lowered in the hottest days of 

 summer to a degree even inferior to that of the external air. 

 The advantage in obviating the wear of wood-work, and 

 the breakage of glass, is manifest. The ventilation of the 

 house for forcing Peaches and Nectarines is also provided 

 vol. vi. 3 D 



