LIGHT. The philosophical consider ation of this imponderable element, as it used to be termed, but more properly now an affection of the ether pervading all space, does not belong to a treatise on the Useful Arts. The practical applica tions and various kinds of artificial lights are those points only which can be touch ed on. Under the articles Candle, Gas, and Lamps, the subject of artificial light has been alluded to. It is proper here to note a few other forms : of these the Drummond Light stands foremost. This light arises from exposing a globule or pea of lime to ignition in a blow-pipe, consuming oxygen and hydrogen. It resembles the focus of a reflector in the sun, and has already been applied to the microscope as a substitute for the sun, and by Lieut. Drummond to the illumi nation of light-houses, instead of Argand burners. The ignition lasts from 15 to 25 minutes, when new globules are in serted. From a small ball, only three eighths of an inch in diameter, so bril liant a light is emitted that it equals in quantity about 13 Argand lamps, or 120 wax-candles ; while, in intensity or in trinsic brightness, it is 260 times that of an Argand lamp. Some idea of its in tense light may be gained from the fact that when the Ordnance Survey of Ire land was being made, it was necessary to have a fixed point of observation, which might be seen at some distance. This light was usually placed on a hill, and with the telescope its light in the day time was discernible 80 miles off. In revolving lights, such as that of Beachy Head, England, there are no less than 80 reflectors, 10 on each side. A single re flector, therefore, illuminated by a lime ball, for each of these 10 is 26 times greater than that of the 30. This method was tried lately at Purfleet, off the En glish coast, in a temporary light-house, erected for the purpose of experiments by the Corporation of the Trinity-house, and its superiority over all the other lights with which it was contrasted was fully ascertained and acknowledged. On an evening, when there was no moon light, and the night dark, with occa sional showers, the appearance of the Purfleet light, viewed from Blackwell, a distance of 10 miles, was very splendid. Distinct shadows were discernible, even on a dark brick-wall, though no trace of such shadows could be perceived when the other lights, consisting of seven re flectors, with Argand lamps, and French lenses, were directed on the same spot.
Another striking and beautiful effect, peculiar to this light, was discernible when the reflector was turned, so as to be itself invisible to the spectator ; a long stream of rays was seen issuing from the spot where the light was placed, which illuminated the horizon to a great distance. As the reflector revolved, this immense luminous cone swept the hori zon, and indicated the approach of the light, long before it could itself be seen from the position of the reflector.
The same balls have been substituted for sunshine, by Carey, of London, in very powerful microscopes, and are con stantly on exhibition in museums. The Drummond Light is well adapted for the Magic Lantern illustrations.
Gillard .Light.—M. J. P. Gillard, a French gentleman, has taken out a pa tent in England, in 1849, for improve ments in the production of heat and light in general.
The patentee's invention consists in certain apparatus and processes for pro ducing hydrogen gas, by the decompo sition of water, and its application to heat and light. The means and pro cesses by which he obtains this gas are : 1. By the incandescency of iron. 2. By carbon. 3. By magnesia.
His improved process for rendering hydrogen gas illuminating, is by causing a small jet of lighted hydrogen to pass through a burner (the holes very small) on a thin strip of platinum wire, the threads being excessively fine, and of graduated section, proportioned to in tensity of the pressure of the flame and the burning hydrogen,—a very powerful light is thus produced. The platinum threads are immediately heated to such whiteness that the luminous refulgence is extraordinarily brilliant. Besides pla tinum, other unalterable and unoxidizable metals may be employed. The wick must be of the shape necessary to agree with that of the jet of hydrogen,—it may be tha of a cone, or any other figure, according to the size which the gas takes when it is allowed egress from the burn er; the wick must be made more or less strong, according to the greater or less intensity of the heat to which it is ex posed. The burner and wick may be modified in their shape,—the patentee does not limit himself as regards the strength, the length, or the height of the wick, provided the principle of his in vention be retained.