The first time that a photograph was taken by this light was at Manchester in the spring of 1864 by 31r. Brothers and Dr. Roscoe. That the magnesium light, in a more or less modified form, must prove of extreme value to photog,Taphy cannot be called in question. Besides overcoming the obstacle of unsuitable weather for the employment of sunlight, it may be applied both for the exploration and the photography of various dim structures, underground regions, etc., such as the interior of the pyramids, of cata combs, natural caverns, etc., which could not otherwise be examined or photographed. Prof. Piazzi Smyth, the Scottish astronomer-royal, dating froin the east tomb, great pyra mid, Feb. 2, 1865, writes as follows: " With any number of wax candles which we have yet taken into either the king's chamber or the grand gallery, the impression left on the mind is merely seeing the candles and whatever is very close to them,*so that you have sniall idea whether you are in a palace or a cottage; but burn a triple strand of magne sium wire, aud in a. moment you see the whole apartment, and appreciate the grandeur of its size and the beauty of its proportions." 31. Madar is said to have taken a series of photographs of the catacombs of Paris; various artists are busy practicing on monu ments in obscure recesses of continental churches; and in different parts of England •caves of prehistoric interest either have been, or are about to be, photographed by this light. For portraiture, it is found to be less successful than was at first expected, owing. to the intense light within a few feet of the sitter's eyes causing a contraction of the facial muscles.
Objectors to the application of such lights NI- the lighting of large buildings and thoroughfares maintain that, while light derived from oil or coal-gas, in which carbon constitutes the ignitible solid, possesses a power of diffusibility which renders objects not directly opposed to the course of the rays MOM or less distinctly visible, the electric, lime, and magnesium lights possess less of this diffusiveness; their rays being appar ently projected with a force and velocity which interfere with the power of diffusion. Ax object placed in the direct course of the rays is splendidly illuminated, and the rays are projected to an immense distance; but the shadows cast by intervening objects are intensely black, and the rays seem to pass through the atmosphere without producing much effect, except upon those parts on which they directly fall.
1Ve may now state some of the advantages which arise from the use of tlie magne sium light. Its color approaches very much nearer to daylight than that of the light from oils, candles, or coal-gas. As compared with the sun, its luminous intensity is but its chemical intensity is and this high actinic power makes it specially valu able for photographic purposes. Although it does not nearly equal the electric light as an illuminating agent, like it the magnesium light gives off no noxious vapors. But as It burns, white clouds of the vapor of magnesia are formed which would be more or less troublesome in private rooms. This objection is said to be to some extent removed, without diminishing the brilliancy of the light, by alloying with zinc; and at any rate, it would scarcely at all interfere with its use in large public buildings. Still less would
it do so when the light is burned in the open air.
There is, however, not much hope of the magnesium light successfully competing with the electric light for the illumination of large buildings, streets, or even of ocean steamers. Recent trials with the electric light at the British museum and other places have now proved conclusively that wherever a great deal of light is required, gas is beaten out of the field on the score of economy. As respects the maintenance of arr. equal amount of light, gas is 20 times more costly, a difference which will speedily cover the original expense of the necessary electrical apparatus. The magnesium light, on. the other hand, is much more costly than gas; and although the ores which could be used as a source of magnesium are very abundant, yet any probable cheapening of the process of extracting the metal from these is not likely to make the light a very economical one. Still, for any.purpose where, for a comparatively brief time, a very intense light is required, magnesium wire or ribbon has about it almost the simplicity of a wax taper; nor are the lamps at all complex by which the metal may be burned for hours continuously.
Two kinds of magnesium lamps are made. In one of these kinds, wire or thin. ribbon of the metal is coiled about a reel or bobbin. From this reel the ribbon is drawn by means of two small rollers and projected through a tube to the focus of a metallic reflector, where it passes through the flame of a spirit-lamp to insure its continuous combustion. These rollers are kept in motion either by an operator turning a small. wheel, or in the more expensive forms by clock-work. In the other kind of lamp the magnesium is used in the form of dust, which is mixed with fine dry sand in the propor tion of one of the former to tWD of the latter. This mixture is placed in a funnel-shaped reservoir, and eonducted, by means of a narrow tube provided with a stop-cock, to tjie flame of a spirit-lamp which serves to ignite and maintain the flame of the powdered magnesium. If nitrate of strontia be substituted for sand, a splendid red light is pro duced, and in this way, by using other chemicals, various colors can be obtained.
It was about the year 1864 that magnesium was first made on a commercial scale,, and it is found that the demand for it, although not decreasing, is scarcely at all extend ing. It is almost wholly used for burning in photographic lamps, for flash lights, and. for fire-works. It has been attempted to make magnesium useful for other purposes. Various alloys have been made with it and other metals, such as lead, tin, zinc, cadmium, and silver; but they are all brittle and liable to change. It is very doubtful, therefore, if any of these alloys will become useful in the arts, and the metal itself is. scarcely likely to be available in the construction of objects of ornament or utility, since, when exposed to damp, it soon becomes coated with a film of hydrate of mag nesium.