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be seen that the fresh cold air is discharged into the room about 

 three or more feet from the floor, thus causing it to diffuse over 

 the whole of the room, preventing cold draughts at the floor. 

 When t)ie fire-place is not sufficient to carry off all impure ah, 

 artifice again supplies the want in the shape of sunlight ventil- 

 ators, grids near the ceiling, or as Fig. 1 shows, a bell-mouthed 

 funnel D in the wall with a connecting tube E carried to the 

 cliimney or outer air. This funnel and tube may be fixed over 

 the ornamental centre piece above the gaslight, as shown at F 

 the funnel, G the tube, also in Fig. 1. For drawing bad air 

 fi'om large rooms the Cowl invented by Mr. Boyle is very per- 

 fect and free in its action. It is connected with the tube before 

 named, and fixed in the outer air and the least breath of air 

 is sufficient to draw off the impm-e gas from the room. There 

 are also many other methods of supplying fresh and withdraw- 

 ing bad air from rooms, but space will not allow of them being 

 named. The noxious gases caused by breathing differ greatly 

 from those given off from decayed animal and vegetable matter, 

 but all these must be guarded against. The highest parts of 

 a town are those where the presence of sewer gas is mostly 

 felt, therefore the ventilation of the main and house drains must 

 be closely looked to in these parts, of course not neglecting the 

 lower parts. Fig. 2 shows the common method of draining a 

 court or back street with back yards at each side. A is the 

 main drain, ending at B, and as it is to this end, as being 

 the most elevated part of the sewer, that the sewer gas makes, 

 it becomes therefore imperative to relieve this end and so pre- 

 vent the gas forcing its way up the house drains and into the 

 houses. To effect this a pipe C, is carried fi-om the end of the 

 sewer to the nearest house up which an iron pipe D is carried 

 above the roof, at its lower end connected with an earthen pipe 

 C. This pipe D is surmounted by one of Boyle's Cowls (before- 

 named) which draws all gas out of the sewer, and if the sewer 

 A is connected with the cross main sewer by means of an open 

 grid manhole, fresh air is constantly drawn through the sewer 

 keeping it perfectly free from bad gases. The rain pipes F.F. 

 on Fig. 2, also act as ventilators to the sewer A, and one of 

 these rain pipes should be fixed for, at most, every four houses ; 

 no trap must be fixed in the branch drains connecting them 

 with the sewer, but they must have a clear course for the whole 

 length of both rain pipe and branch di'ain G. 



Now come the questions. How would the gas get into the 

 houses, if not drawn off? And, how prevent the gas getting 

 into the houses at all ? — First then, sewer gas gets into houses 

 through defective drainage, porous walls, and in a many other 

 ways. Various " Traps " have been invented, to stop sewer gas, 

 with " water seals " varying in depth from 3 to 6 inches. It is at 



