Fig. 20.
the flue and caused the smoke to enter into the whole of the eight rooms.
The chimney-stack might possibly be lowered, and it certainly could be constructed without chimney-pots, but each separate flue must have its own outlet. A design for this, one that should take away the open character of the flue, and fit the stack, possibly for the Mansard roof, is here given.
In fig. 21, a a are the flues, delivering their smoke into a large ventilating flue, b. The warm smoke would induce a current of air to enter at c: any current will have a tendency to draw another with it, so that the smoke leaving the flues c c would be taken out at d by the current of air at c.
Fig. 21.—The ventilating flue.
This is the principle upon which all the best ventilating chimney-pots, tall-boys, and cowls are made, and it is a very sure one. The jet of steam in the funnel of the locomotive, drawing the smoke from the fire, and creating a draught, is adopted on the same principle.
In scientific language, the established law both of pneumatics and hydraulics is that when two currents of fluid matter passing in the same direction, but in separate channels, arrive at any point of confluence, the stronger current draws the other along in its course, and with a considerable portion of its own velocity. Thus the force of the wind, which checks in other instances the action of a chimney-draught, is made to produce a stronger draught, exactly in proportion to the violence with which it blows.
Returning to fig. 21, a current of air, instead of coming in at the opening c, might come in at d. It would then have a tendency to blow down the flues a a: to prevent this, the opening d could be closed, and an upright stalk placed at e,—this should have a downward shaft, a place for soot, and a sweeping door.