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or fine brass wire gauze might be inserted in the cornice. The foul air would pass through this into the spaces between the joists, when the sound boarding and pug. ging will preventits ascending into the upper
From these spaces it would pass into a cast-iron channel running round the room, which would communicate with the chimney or air flue, or in some cases directly
with the outer air. The openings into the chimney or air fue must be fitted with valves, as before.
I believe it would be easy to construct a chimney having all the advantages of a chimney and air flue combined.
A tube should be inserted in the brick trimmer giving immediate communication with the fire above, which, when lighted, would aid the ventilation of the lower room.
All large houses should have a special ventilating shaft, communicating by means of pipes and valves with every room in the house. If thermo-ventilation alone is intended, a fire must be kept burning at the base of the chimney, the only supply of air to which must come through the tubes.
Some day, perhaps, we may have ventilating shafts for every street or block of houses. We provide for the carrying away of foul water, why not of foul air? The one is just as harmful as the other. Perhaps, too, though this belongs rather to warming than ventilation, we may some day see but one fire to each house, and even one chimney. Nay I will go further, perhaps one chimney to a great number of houses, perhaps even one to a town! This may seem a speculative flight; but had coals been very dear instead of cheap, I feel sure our present wasteful system would not have lasted long.
Before quitting the subject of house ventilation, I will notice one fruitful source of annoyance, which is often closely connected with defective ventilation, I mean smoky chimneys. Want of air causes perhaps more chimneys to smoke than any thing else, and before any one sets to work to alter the chimney in any respect, it is better to see whether it is not more air that is wanted. This may be easily done by trying the fire with a door or window open, and with the same shut. If in the latter case the fire smokes, while in the former it does not, then want of air is the cause. Care must, however, be taken, as to what window is open, as gusts of wind or a cross draught will often cause the fire to smoke.
For churches, schools and factories, thermo-ventilation may be used, but probably the fan, or blowing wheel, will, in many cases, be more efficient and economical,
I believe it is in use in some buildings in London with very satisfactory results.
Its useful effects will vary with the size of the wheel and the speed at which it is driven, and in designing a fan it should
be borne in mind, that a large fan and low speed is generally better than a small one and high speed, chiefly on account of the vibration caused by gearing running at great velocities.
The motive power may be either steam, water, or a weight which can be wound up as occasion may require.
It is impossible here to even refer to many noxious manufactures, chemical and otherwise. But of this we may be sure, that if they are prevented by law from polluting the atmosphere, the science of chemistry is quite equal to finding a remedy, and even to converting the noxious fumes into useful products.
There is an objection to thermo-ventilation, which does not apply to the fan, viz., that, as it usually depends for action upon the difference in temperature between the inner and outer airs, 80 in summer it may come to a stop, or be even reversed.
This objection is not of much weight, as people are far oftener out in the air in summer, and at night when gas or candles are lighted ventilation would commence again.