The ventilating pipe or chimney is a copper tube, 4 inches in diameter, not, however, in one length, but divided into three or four pieces: the lower end of each of these pieces, for about 1½ inch, is opened out into a conical form about 5½ inches in diameter at the lowest part. When the chimney is put together, the upper end of the bottom piece is inserted about ½ an inch into the cone of the next piece above, and fixed there by three ties or pins, so that the two pieces are firmly held together; but there is still plenty of air-way, from the surrounding atmosphere into the chimney between them. The same arrangement holds good with each succeeding piece. When the ventilating chimney is fixed in its place, it is adjusted, so that the lamp-chimney enters about ½ an inch into the lower cone, and the top of the ventilating chimney enters into the cowl or head of the lantern.
With this arrangement, it is found that the action of the ventilating flue is to carry up every portion of the products of combustion into the cowl; none passes out of the flue into the air of the lantern by the cone apertures, but a portion of the air passes from the lantern by these into the flue, and so the lantern itself is in some degree ventilated.
The important use of these cone apertures is, that when a sudden gust, or eddy of wind, strikes into the cowl of the lantern, it does not have any effect in disturbing or altering the dame. It is found that the wind may blow suddenly in at the cowl, yet the effect never reach the lamp. The upper, or the second, or the third, or even the fourth portion of the ventilating Hue might be entirely closed, yet without altering the flame. The cone junctions in no way interfere with the tube in carrying up all the products of combustion; but if any downward current occurs, they dispose of the whole of it into the room, without ever affecting the flame. The ventilating Hue is, in fact, a tube which, as regards the lamp, can carry everything up, but conveys nothing down.
In lighthouses with many separate lamps and reflectors, the case is more difficult and the arrangement more complicated, yet the conditions before referred to are more imperatively called for, because any departure from them was found to have greater influence in producing harm. The object has been attained thus:—A system of gathering pipes has been applied to the lamps which may be considered as having the different
