a, the vessel of condensed gas; b b, the reflectors, placed at suitable angles to accumulate the light upon a bull's eye magnifier fixed in front, but removed in the drawing to show the interior of the lantern; c, the screw cap of the lantern; d, the alkaline solution; e, the jet pipe; f, portions of the shield frames of the tunnel; h, accumulation of mud and earth as it may be supposed to have entered the tunnel.
The cut on p. 43, represents one of the many ways in which the "march of mind" in the present day accelerates the march o the body; the subject is a "stirrup lantern," intended, in the words of Scripture, as a "light unto our feet, and a lamp unto our paths." The stirrup lantern is a small square lantern, fixed at the bottom of a stirrup by means of two screw rings on each side, as exhibited in the drawing, and by unscrewing them, the lantern may be detached from the stirrup when requisite. The lamp part is so contrived that no oil can be spilt, nor the steady light which is thrown across the road before the horse's feet be at all impaired by any motion of the horse. The front part, as shown in the drawing, is of glass, through which is seen the lamp, burner, and wick; behind, there is placed a reflector for transmitting the light to the front. It is supplied with a constant current of air, by means of apertures, in a sort of double casing, which is so disposed as to prevent any gust of wind from extinguishing the light.
Amongst the numerous contrivances for rendering lamps ornamental, is a very singular one, which we must briefly notice: it consists in surrounding the light by screens of ground glass, on which are painted various elegant devices; these screens are suspended upon a fine pivot, in the same way as a common chimney cowl, and have fixed across their upper orifice a number of oblique vanes or fans; and the current of heated air from the lamp, impinging upon these vanes, imparts to the screens a slow rotatory motion. The pleasing effect of crystal chandelier ornaments in refracting the rays of light is well known; but the chandelier makers have hitherto principally devoted their attention to increasing the number of reflecting and refracting surfaces without paying much regard to their form, magnitude, or position with respect to each other. M. Osier, of Birmingham, however, has lately introduced a great improvement in this branch of the subject; instead of a great number of detached crystal drops, he forms a complete casing for the light by ranging a number of square or triangular prisms in a cylindrical or conical figure, the sides of the prisms touching each other, and their ends being connected by various ingenious means, for which he has a patent.
The effect thus produced by the large surface of the prisms is exceedingly brilliant and splendid.
We shall conclude this article by a description of that admirable invention of Sir H. Davy, the "safety lamp," by the aid of which the hazardous occupations of the miner are now carried on with considerably less difficulty, and with infinitely less danger, than before this invention. The gases extricated in mines (which are destructive to animal life) are of two kinds, and are by the miners called the choak damp, and the fire dump; the former consists for the most part of carbonic acid gas, hovers about the lower parts of the mine, and extinguishes their lights; and the latter, which is simply hydrogen gas, occupies the superior spaces, and involves incalculable mischief, from the combustion produced by its contact with the flame of the miners' candles. The consequences resulting from the frequent explosion of this inflammable air, have been lamentable and tremendous in the highest degree; and whilst a source of the greatest terror to the persons most intimately affected by its operations, it has excited the deepest sympathy and commisseration in the general mind.
To remove an evil so dreadful in its nature, Sir H. Davy applied his energetic and compre hensive mind to the discovery of some means by which these saddening calamities might be averted, and after numerous experiments, devised the safety lamp, an invention that must ever rank him high among the benefactors of mankind.
To afford a clear idea of the nature of the lamp, we shall avail ourselves of the language of Dr. Ure, who has treated it, and the points relatively consequent upon it, in a very masterly manner. "In the parts of coal mines where danger was apprehended from fire-damp,miners had been accustomed to guide themselves, or to work, by the light afforded by the sparks of steel struck off from a wheel of flint. Buteven this apparatus, though much less dangerous than a candle, sometimes produced explosions of the fire-damp. A perfect security from accident is, however, offered to the miner, in the use of a safe lamp, which transmits its light, and is fed with air, through a cylinder of iron or copper wire gauze; and this fine invention has the advantage of requiring no machinery, no philosophical knowledge to direct its use, and is made at a very cheap rate. The apertures in the gauze should not be more than l-20th of an inch square. As the fire-damp is not inflamed by ignited wire, the thickness of the wire is not of importance, but wire from l-40th to l-50th of an inch in diameter is most convenient. The cage or cylinder should be made by double joinings, the gauze being folded over in such a manner as to leave no apertures.
When it is cylindrical, it should not be more than two inches in diameter; for in larger cylinders, the combustion of the fire-damp renders the top inconveniently hot; and a double top is always a proper precaution, fixed one-half or three-fourths of an inch above the first top. The gauze cylinders should be fastened to the lamp by a screw of four or five turns, and fitted to the screw by a tight ring. All joinings in the lamp should be made with hard solder; and the security depends upon the circumstance, that no aperture exists in the apparatus larger than in the wire gauze." The parts of the lamp are - A, the brass cistern which contains the oil, pierced near the centre with a vertical narrow tube, nearly filled with a wire which is recurved above, in the level of the burner, to trim the wick, by acting on the lower end of the wire, with the fingers: it is called the safety trimmer. B, the rim in which the wire gauze cover is fixed, and which is fastened to the cistern by a movable screw. C, an aperture for supplying oil, fitted with a screw or cork, and which communicates with the bottom of the cistern by a tube; and a central aperture for the wick. D, the burner, or receptacle for the wick, over which is fixed the coil of platinum wire.