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a distance equal to the difference in height between a column of air 10 ft. 6 in. high at 62 deg., in the case I have assumed, and the same air at 32 deg.
This difference will be equal to .643 of a foot, and the speed of the entering current will, by the rule for falling bodies, be 6.43 ft. per second.
Assuming that all the air enters through one opening, then about 8 sq. in. would be sufficient. It will be obvious, however, that it is not advisable to admit' air at so high a velocity as this, nor would one inlet be so efficient as several."
I would propose, then, for existing rooms, that the inlets should be made in the side walls, near the floor, and in as many different sides of the rooom as its situation will allow. That these be made larger towards the room, and that they should be enclosed by metal gratings made ornamental on the outer and inner faces. The sketch marked A will show generally what I mean.
There is one point to which I would call your particular attention, and this is the
fine wire gauze screen shown just behind the ornamental front. This serves a very useful purpose, for it screens and breaks up the entering current of air, preventing all drafts, and, if the openings have sufficient area, allowing the incoming air to mingle 80 gently with that now in the room, that its presence is not felt save in a pleasant way.
I attach great importance to this screen, and to the size of the openings.
We must now proceed to consider the best position for the exit.
I think a little consideration will show us that the heated chimney affords the best possible means under the circumstances. By causing the foul air to escape into the chimney we increase the ventilating power
FIG. 2.-ELEVATION.—A is the grating.
very considerably. We have no longer to deal with the small difference before mentioned, but may calculate upon the whole height of the chimney, above the opening, through which the foul air enters it, and have the difference between this column of air highly heated as it is, and that of
another of the density of the outer air, as the force at our disposal.
Care must be exercised in the choice of a valve to close this opening against down draft. The best which has come under my notice is formed of a series of leaves or flaps of mica enclosed in a metal case. The flaps are very light, and, being hung from the top, are absolutely secure against return currents. The front may be made as ornamental as can be desired.
The heated and spent air from the gas light should be conveyed away immediately when possible.
The ornamental flower which is commonly placed in the centre of the room may be pierced through. The opening thus formed being boxed in between the joists with thin sheet metal connected with a tube for conveying the waste gases into the chimney or outer air.'
The register of the fire grate will form a regulator, by closing or opening which the draft through the escape valve may be increased or diminished.
Exercise of proper skill and judgment in