284 



VENTILATION. 



itself rendered water-tight at bottom, and 

 kept filled with water as high as half the 

 diameter of the return-pipe. The water 

 is, in consequence, kept warm, and gives 

 out a genial vapour to the house all 

 along its front. The air discharged by 

 the pipe into this chamber becomes con- 

 siderably heated, and, in its ascent into 

 the house, carries with it more vapour 

 than it brought in, because it naturally 

 takes some with it from the water over 

 which it passes. One of these air-tubes is 

 placed under the middle of each alternate 

 sash, the remaining sashes having a simi- 

 lar air-pipe, which, instead of discharging 

 itself into the shallow tank, passes through 

 it and under the pit, rising at b by the 

 side of the footpath, and discharging its 

 supply of air through a perforated cover- 

 ing. The houses where this mode of 

 aeration is practised have a range of 

 cellars behind well lighted and venti- 

 lated. From these an orifice is cut through 

 the back wall, as shown at c, through 

 which a supply of air, far from cold, enters 

 the house close to the footpath; and, 

 where no cellars exist, the pipe may be 

 supplied with air from the surface, as 

 shown at /. By these contrivances, abun- 

 dance of ventilation is produced during 

 winter and spring ; and during summer, 

 when more may be desirable, especially 

 for lowering the temperature, the front 

 sashes d, and the usual top ventilators e, 

 are opened in addition. 



On a somewhat similar principle, in 

 houses heated by smoke flues, which in 

 general run parallel with the front of the 

 house, and not far distant from it, fire- 

 clay tubes may be brought through the 

 parapet wall, extending through the flue 

 close to its bottom, having one end open 

 to the atmosphere, as 

 shown at a, in fig. 380, 

 and the other to the at- 

 mosphere of the house 

 within, at b. A circula- 

 tion would take place, 

 and a supply of genially 

 heated air be thus drawn 

 in, which could be regu- 

 lated to any extent by 

 a revolving ventilator 

 being placed on the orifice of each tube 

 within the house. The quantity of air 

 obtained by this means would be very 

 considerable, and, of course, greater as 



Fig. 380. 



Fig. 381. 



the number of tubes was increased, which 

 latter we would prefer to having them 

 fewer in number and of larger calibre. 

 As a homely illustration of this, we may 

 observe, that any one may satisfy himself 

 of the operation by putting his hand to 

 the key-hole of his sitting-room door. If 

 the passage without be cold, and the 

 room within warm, the draught of air 

 rushing in, even at that small aperture, 

 will be found very considerable; and this 

 the more so, as the temperature in the 

 room and that of the passage happen to 

 differ. Were it not for the pressure of 

 the cold air from without, even with our 

 best fitted doors and windows, our warm 

 rooms would be unbearable to human 

 beings; and even our fires would cease to 

 burn. 



There is also another mode of ventila- 

 tion upon the same principle which may 

 be adopted with great advantage. The 

 annexed diagram, fig. 

 381, represents part 

 of the front of a forc- 

 ing-house, the para- 

 pet of which, under 

 the ground level, is 

 built of piers, and 

 lintelled over with 

 stones, which form the 

 plinth (a) on which 

 the superstructure 

 rests. Between these 

 piers cast-iron boxes (b) are placed, 2 feet 

 long and 3 inches in diameter, the one end 

 open to the external air just below the 

 plinth, and fitted with a lid to regulate 

 the admission of the cold air. The lower 

 end is open, and through these boxes the 

 air is partly forced down by its own gra- 

 vity from b, and partly drawn down by 

 the heated air at c rising into the house 

 and creating a sort of vacuum, which the 

 cold air rushes in to fill up. The hot- 

 water pipes are, as in the former case, 

 laid in an open flue, the bottom of which, 

 at c, is meant to contain water, supplied 

 by a small pipe from the cistern over the 

 furnace. The lower pipe is partially 

 sunk in this water, which gives out a 

 genial steam, and increases both the tem- 

 perature and the moisture of the cold air 

 as it passes over it, rendering it fit for 

 coming into immediate contact with the 

 plants. The arrows at d show the direc- 

 tion of the current of air. By a very 



