Fig. 20 is a diagram of the lamps in any building. The street main, M, enters at the main switch, S, and continues from switch to switch, S¹ S¹, and returns to S before it leaves. It is necessary, to guard against any possible extinction, to construct all the switches so that it would be impossible to move the lever without a lamp was lighted; and, should the lamp give out, an equivalent resistance must be automatically inserted. These details have been investigated by Mr. Alexander Bernstein, who has designed a complete system for “series” lighting, and claims for it special economical advantages. It is, however, very doubtful if this plan can be recommended for adoption in private houses; but in public lighting, or in large establishments where an electrician could be kept to look after the fittings and the insulation of the conductors, there should be no more danger, in introducing the high-tension continuous current of 2,000 volts, than there is at present with the 100-volt alternating current, and the relative saving in weight of conductors would be an important item.
Installations on this method have been erected at Messrs. Brunner and Mond’s alkali works, and in several large factories in the United States where lights had to be distributed over a considerable area; the system has not, however, come into favour for central-station work.
This method of using a high-tension current has already been referred to in connection with house-to-house lighting at Brighton, it was first employed for the street lighting of Chesterfield by the Brush Company. The electric lighting of the town of Temesvar, in Hungary, is on a far larger scale, and has, from November 1884, successfully superseded a combination of gas for the more important streets, and petroleum for the outlying ones, the total cost of which was 26,480 florins per annum. A twenty-four years’ concession was given to the International Electric Company, the plant remaining their property at the expiration of the term, subject to purchase by the municipality at their own valuation. The public lighting is stipulated to be effected by means of 731 glow lamps of the intensity of 16 candle-power; but the option is given to the company of switching out a fixed proportion of these lamps at 11.30 P.M., or of leaving the whole number in operation with their light-intensity reduced from 16 to 8 candle-power from 11.30 P.M. till dawn. The total number of lighting hours per annum is 3,597½ for the lamps which are in operation from dusk until dawn, and 1,816 for those which are extinguished at 11.30 P.M. The price fixed in the concession for public lighting is 1·5 kreutzer per 16 candle-power lamp per hour, equal to 53 florins 95 kreutzers per lamp per annum of 3,597½ hours, or 27 florins 24 kreutzers per lamp per annum of 1,816 hours. The company has found it more convenient to exercise the option reserved to it, of keeping all the 731 lamps in operation from dusk till dawn, reducing their light-intensity to 8 candles after 11.30 P.M.; and the municipality has agreed to pay a round sum of 29,000 florins (£2,416 13_s._ 4_d._) per annum for this lighting, and 41·95 florins (£3 10_s._) per annum for each additional lamp worked in the same way. Comparing these figures with what precedes, it will be found that the electric lighting of the streets now in operation costs 2,520 florins more than it did on the former plan of combined lighting, partly by gas and partly by petroleum. On the other hand, the streets are lighted throughout with 16 candle-power lamps from dusk until 11.30 P.M., and with 8 candle-power lamps from 11.30 P.M. until dawn. For electric light supplied to private consumers the concession fixes the price at 1·81 kreutzers per 16 candle-power lamp per hour, or 0·1131 kreutzers per candle per hour, with the right to charge 15 per cent. more for lamps of less intensity than 16 candles. In all these prices the renewal by the company of lamps failing from legitimate wear is included.