488 Draft of Chimneys—Ventilation of Skips. [Book V.

chapter. 2. Increasing the draft of chimneys, as well as preventing themfrom Smoking. Instead of the old fashioned caps of clay or the moveable

ones of iron, let them be made in the form ofthe annexed figure, and either of sheet iron orcopper. A short pipe should be fixed on thechimney, and over it an outer one (shown inthe cut) to turn freely, but as close as possiblewithout touching, that the horizontal one towhich the latter is attached may veer roundwith the wind. The vane V keeps the oppo-site end A to the wind, which enters as indi-cated by the straight arrow, and in passingthrough sweeps over the projection and causesa vacuum in the chimney, as in the blowingtubes already described.

A device of this kind might be made to act in windy weather as a per-petual bellows to blast or refining furnaces, and also to those of steam-boats and locomotive carriages. When used on chimneys of the latter, acontrivance to turn and keep the blowing tube fore and aft, as the carriage isturned, would be required. The joint where the perpendicular tube movesover the fixed one might also be made air-tight by an amalgam, on theprinciple of the water lute. From the experiments with the tubes Nos.206, ’7, ’8, ’9, ’IO and ’13, it follows that if the waste steam of a locomo-tive carriage were discharged over the mouth of the chimney as above,instead of up its centre, the resulting vacuum would be greater.

It is worth while to try whether Wells, mines, and the holds of ships,could not be more speedily and effectually ventilated by a similar devicethan by the common wind sails used in the latter. These displace thenoxious vapors by mixing fresh air with them, but by the proposed planthe foul air might be drawn up alone, while the atmosphere would causea steady and copious supply to stream in at every avenue.

If two or three exhausting tubes, of metal or of any other suitable ma-terial, (whose diameter for a ship of the largest dass need not exceedthree or four inches) were permanently secured in a vessel, their lowerends terminating in or communicating with those parts where noxiouseffluvia chiefly accumulates, and the upper ends leading to any convenientpart of the deck, sides or Stern, so that the blowing part could readily beslipped tight into or over them, the interior might be almost as well ven-tilated, even when the hatches were all down, as the apartments of anordinary dWelling. It appears to us moreover, that a vessel might by thismeans be always kept eharged with fresh and pure air; for the apparatusmight be in Operation at all times, day and night, acting as a perpetualpump in drawing off the miasmata. The only attention required wouldbe, to secure the blowing tube in its proper position with regard to thewind during storms. In ordinary weather its movements might be regu-lated by a vane, as in the figure, when it would require no attention what-ever. The upper side of the blowing part of the tube should be cut partlyaway at the end, so as to facilitate the entrance of descending currents ofwind. See the above figure.

No. 215.