Both air and water being transparent and colourless fluids, their internal motions are not easily discovered by the sight, and when these motions are very slow, they make no impression whatever on any of our senses, consequently they cannot be detected by us without the aid of some mechanical contrivance:-- But where we have reason to think that those motions exist, means should be sought, and may often be found, for rendering them perceptible. If a bottle containing hot water tinged with log-wood, or any other colouring drug, be immersed, with its mouth open, and upwards, into a deep glass jar filled with cold water, the ascent of the hot water from the bottle through the mass of cold water will be perfectly visible through the glass.-- Now nothing can be more evident than that both of these fluids are forced, or PUSHED, and not DRAWN upwards.--Smoke is frequently said to be drawn up the Chimney;--and that a Chimney draws well, or ill;--but these are careless expressions, and lead to very erroneous ideas respecting the cause of the ascent of Smoke; and consequently tend to prevent the progress of improvements in the management of fires.--The experiment just mentioned with the coloured water is very striking and beautiful, and it is well calculated to give a just idea of the cause of the ascent of Smoke. The cold water in the jar, which, in consequence of its superior weight or density, forces the heated and rarefied water in the bottle to give place to it, and to move upwards out of its way, may represent the cold air of the atmosphere, while the rising column of coloured water will represent the column of Smoke which ascends from a fire. If Smoke required a Chimney to DRAW it upwards, how happens it that Smoke rises from a fire which is made in the open air, where there is no Chimney? If a tube, open at both ends, and of such a length that its upper end be below the surface of the cold water in the jar, be held vertically over the mouth of the bottle which contains the hot coloured water, the hot water will rise up through it, just a smoke rises in a Chimney. If the tube be previously heated before it is plunged into the cold water, the ascent of the hot coloured water will be facilitated and accelerated, in like manner as Smoke is known to rise with greater facility in a Chimney which is hot, than in one in which no fire has been made for a long time.--But in neither of these cases can it, with any propriety, be said, that the hot water is DRAWN up the tube.--The hotter the water in the bottle is, and the colder that in the jar, the greater will be the velocity with which the hot water will be forced up through the tube; and the same holds of the ascent of hot Smoke in a Chimney.--When the fire is intense, and the weather very cold, the ascent of the Smoke is very rapid; and under such circumstances Chimneys seldom smoke.