Electric Lighting

The brilliant and dazzling light obtained by transmitting a powerful electric current _between two sticks of carbon was first - discovered by Sir Humphry Davy, who exhibited it in 1813 at the Royal Institution, employing for the purpose a voltaic battery of 2,000 cells. One of the chief obstacles to the earlier introduction of the light was the cost and trouble of maintaining 2 sufficiently strong current by means of aA voltaic battery. Faraday’s discovery of magneto-electric induction furnished aA new source of electricity, and machines founded on this principle were succe ively improved till a larger pattern, commenced by Nollet in 1850, was so far improved by Holmes in 1853 and following years, as to be adopted by the Trinity Board in 1857 for lightouse purposes. Modern dynamos consist e entially of two principal parts, viz., the electro-magnet or magnets, usually fixed, and the armature which revolves. The electro-magnet when excited by the current through its coils creates a magnetic field of intense power. The armature, a coil or collection of coils mounted on a spindle, is revolved in this magnetic field. Powerful currents of electricity are thus obtained, which are collected and directed by various devices. When a number of electric lamps are supplied from the same source they may either be connected in series or in parallel circuit. The former term is applied when the same current goes through all the lamps in succe ion; the latter when the current is divided into branches, one branch going through each lamp. The series arrangement requires a device so that if one lamp be extinguished it does not put out all the others in the same circuit. In the parallel circuit arrangement, the extinction of one or more of the lamps does not affect the brightne in the rest. The Edison system of electric lighting is based on this plan. The Brush system lies at the opposite extreme snd is adapted for supplying a number of arc lamps in series, A system of distribution known as the three wire system has been found very effective in allowing the use of higher electric pre ures, whereby at 1 slight extra cost many additional lamps can be lit from the main leads. For this purpose two dynamos coupled in series.are employed, the mains consisting of two heavy leads — one from the free jterminal of each dynamo — with a lighter middle wire running from the coupling of the dynamos. The lamps a arranged in parallel between each of the outer leads and the middle wire, the function of which is to render the sets of lamps on each side of it independent of each other. Should the number of lamps lit be the Same on each side there is no current in the middle wire, but should there be an exce in the number on one side, then a current equal to the difference of the current in the outer leads flows along it. It is estimated that with incandescent lamps of about 20 candle power each, the light obtained is at the rate of from 200 to 250 candles per horse power in the driving engine, and that in the largest useful size of are lights the light is at the rate of about 2,000 candles. The incandescent light is steady, while the arc is fluttering.