As the cold water of the jar immediately surrounding the bottle which contains the hot water, will be heated by the bottle while the other parts of the water in the jar will remain cold, this water so heated, becoming specifically lighter than that which surrounds it, will be forced upwards; and if it finds its way into the tube will rise up through it with the coloured hot water.--The warmed air of a room heated by an open Chimney Fire-place has always a tendency to rise, (if I may use that inaccurate expression,) and finding its way into the Chimney frequently goes off with the Smoke. What has been said, will, I flatter myself, be sufficient to explain and illustrate, in a clear and satisfactory manner, the cause of the ascent of Smoke; and just ideas upon that subject are absolutely necessary in order to judge, with certainty, of the merit of any scheme proposed for the improvement of Fire-places; or to take effectual measures, in all cases, for curing smoking Chimnies.--For though the perpetual changes and alterations which are produced by accident, whim, and caprice, do sometimes lead to useful discoveries, yet the progress of improvement under such guidance must be exceedingly slow, fluctuating, and uncertain. As to the causes of the smoking of Chimnies, they are very numerous, and various; but as a general idea of them may be acquired from what has already been said upon that subject in various parts of this Essay, and as they may, in all cases, (a very few only excepted,) be completely remedied by making the alterations in Fire-places here pointed out; I do not think it necessary to enumerate them all in this place, or to enter into those long details and investigations which would be required to show the precise manner in which each of them operates, either alone, or in conjunction with others.