"And, lo, the smoke of the country went up as the smoke of a furnace."—Gen. xix.
682. Why does smoke issue in folds and curls?
Because it is pressed upon by the cold air which always rushes towards a rarer atmosphere. It thus illustrates the development of storms.
683. Why do some chimneys smoke when the doors and windows are closed?
Because the draught of air is not sufficient to supply the wants of the fire, and enable it to create an upward current.
684. What is the best method of conveying air to fires?
Tubes built in the walls, communicating with the outer air, and terminating underneath the grates.
685. Why is this the best method of ventilation?
Because doors and windows may then be made air-tight, and draughts across rooms be prevented.