To obviate these objections, Mr. Roberts, of St. Helen's, Lancashire, has introduced some modifications and improvements in the construc tion of the safety lamp, for which he has received a reward from the Society of Arts. To diminish the obscuration occasioned by the first cause, Mr. Roberts proposes that the wire shall be kept bright and polished, by cleaning the cage every night with a soft brush, and the black powder, or smut, which occurs in all coal mines, especially in the neighbourhood of faults; this smut is pulveru lent non-bitumenous coal, sufficiently hard to re move the rust from the surface of the wire, without materially wearing the wire itaelL As the lamp is at present constructed, the oil will run out of the cup or receptacle in which iit is placed, if the lamp is laid in a horizontal position, an accident which frequently occurs on account of the lamp being rather top heavy. When this happens, the gauze becomes smeared over with viscid oil, which causes the coal dust floating in the air of the mine to adhere to it, and in a short time to fill up, more or less, the meshes of the gauze. By merely shaking or tapping the lamp, the dust will not be dislodged and if the miner attempts to clear his lamp by blowing through the wire gauze, he runs the risk of putting out the light, and, after all, very imperfectly clears the meshes ; there is also, perhaps, some risk of forcing the flame through the meshes on the opposite side, and of producing an explosion, if the sur rounding air is inflammable. In Mr. Roberts's lamp the overflow of the oil is impossible, on account of the dome-shaped cover which surrounds the wick ; the dust, therefore, that settles on the gauze may be dislodged by a mere tap of the finer, or what would perhaps be better, by the application of a small brush similar to that which soldiers carry to clear the pan of their muskets, and which might be attached by a bit of small chain to the handle of the lamp. Fog. 1, on the preceding page, represents • section of the lampf p,
and wire gauze q q; r r, a screwed cap, with a hollow dome s ; it screws Into the neck, t t, of the lamp ; the dome rises a little above the neck bolder ts, having an opening at top to let the wick and trimming wire e, rise through. This dome serves to catch and retain any oil that maybe spilt by shaking the lamp, or knocking it over, thereby protecting the wire gauze q from being smeared : w ands, two locks, the former to secure the cap q, and the latter to secure the wire gauze q from being removed. Fig. 2, a section of the cap and dome, r r s, separate from the lamp ; the wire gauze fits into the cavity y y, around the dome s ; a a, two of the four wires which serve to hold the wire gauze.
Mr. Bonner, of Monkwearmouth, Durham, has a patent for an improvement upon the safety lamp, which consists in a means of increasing the hght of the lamp, and also of extinguishing it instantaneously. The mode of increasing the light is as follows :—Instead of introducing a wick in the centre of the lamp, as is usually practised, be introduces a series of small wicks round a centre tube, and by lighting one, two, or more wicks at a time, little or much light is obtained. The means of instantly extinguishing the light consists in a metal cap, or extinguisher, suspended within the wire gauze tube by a pin or catch ; upon withdrawing the pin the extinguisher falls over the wick and the light is put out.
In Mr. Murray's safety lamp the wire gauze tube is suspended by two con centric tubes of strong glass, the space between the two tubes being nearly filled with water; by this means a much greater degree of light is obtained, but we are not sure that the risk is not also greater than when a wire gauze tube is employed.