ELECTRIC LIGHT. Among the nume rous practical applications of electric power, nol the least curious is that of maintaining a steady light for public streets. The scheme has not yet assumed a fully satisfactory posi tion ; but it is not improbable that it may do so ere long.
In 1846 Messrs. Greener and Staite patented the electric light, as a means of illuminating public, thoroughfares and buildings. The plan described by the patentees involves the use of small lumps of pure carbon, enclosed in air-tight vessels, and rendered luminous by currents of galvanic electricity ; pieces of platinum are also mentioned as being fitting I substitutes for the carbon. The idea was not new ; but the patentees claimed to have placed it in a more practical form than it had before assumed. During the year 1847 Mr. Staite exhibited his electric light in many parts of the country ; and in a lecture on the sub ject at Newcastle, he gave the following sta tistical estimate of its capabilities With a battery consisting of 40 small cells in series, the light was equal to 380 tallow candles, 300 wax candles, or 64 cubic feet of gas : this being effected by the consumption of little more than f of a lb. of zinc per hour. The relative cost was by the electric light Id., gas Od. or 8d., tallow candles 7s. 6d., and wax candles 12s. ad. per hour.' We may remark however that this mode of comparison is open to many fallacies.
In 1848 the electrio light was exhibited very frequently in different parts of London. The general arrangement is as follows :—Two small cylinders of carbon are placed with their ends nearly in contact, being distant apart some fraction of an inch, which is made to depend for its amount on the size and pur pose of the apparatus. A train of wheels is attached to the machine to keep these carbon points always at the same distance apart during their slow combustion. There are also the galvanic apparatus and the wires ; and the principle of action depends on the fact that the galvanic circuit is not completed unless the fluid can traverse the small dis tance from one piece of carbon to the other : the resistance which the carbon offers to the' transit occasions the evolution of a most in tense light. The mechanism by which the
points are kept at such a distance as to give continuous instead of an intermitting light, is very ingenious, and such as had not previously been applied.
In the same year an electric light of some what similar character, but differing in many working details, was introduced at Paris, and was afterwards exhibited also in London, by MM. Achereau and Fourcault. Dnring 1840, in a lecture by Mr. Grove at the Royal Institu tion, and at the meeting of the British Asso ciation in Birmingham, as well as in scientific and practical papers in the public journals, the merits and demerits of the electric light were discussed at considerable length.
In Mr. Allman's electric light, brought under public notice in 1850, the mechanism differs from that of the older form in main taining the carbon points always at a proper dis tance apart. When more of the electric fluid is passing than is necessary to maintain the re quired intensity of light, the mechanism so adjusts itself as to bring the carbon points farther apart; whereas, when the electric fot ce is below its proper limit, the points approach more closely. The apparatus possesses there fore something of the self-governing or self adjusting power which is so admirably exem plified in modern steam-engines. There are many circumstances which seem to indicate that we are not far removed from the period when light produced by electric agency will he rendered practically available in manufac tures and the arts of life. •