There has lately been held, at No. 31 Lombard Street, London, a private exhibition of the Holmes and Burke primary galvanic battery. The chief object of the display was to demonstrate its suitability for the lighting of railway trains, but at the same time means were provided to show it in connection with ordinary domestic illumination, as it is evident that a battery will serve equally as well for the latter as for the former purpose. Already the great Northern express leaving London at 5:30 P.M. is lighted by this means, and satisfactory experiments have been made upon the South-western line, while the inventors give a long list of other companies to which experimental plant is to be supplied. The battery shown, in Lombard Street consisted of fifteen cells arranged in three boxes of five cells each. Each box measured about 18 in. by 12 in. by 10 in., and weighed from 75 lb. to 100 lb. The electromotive force of each cell was 1.8 volts and its internal resistance from 1/40 to 1/50 of an ohm, consequently the battery exhibited had, under the must favorable circumstances, a difference of potential of 27 volts at its poles, and a resistance of 0.3 ohm.

When connected to a group of ten Swan lamps of five candle power, requiring a difference of potential of 20 volts, it raised them to vivid incandescence, considerably above their nominal capacity, but it failed to supply eighteen lamps of the same kind satisfactorily, showing that its working capacity lay somewhere between the two. A more powerful lamp is used in the railway carriages, but as there was only one erected it was impossible to judge of the number that a battery of the size shown would feed. Engineering says the trial, however, demonstrated that great quantities of current were being continuously evolved, and if, as we understood, the production can be maintained constant for about twenty-four hours without attention, the new battery marks a distinct step in this kind of electric lighting. Of the construction of the battery we unfortunately can say but little, as the patents are not yet completed, but we may state that the solid elements are zinc and carbon, and that the novelty lies in the liquid, and in the ingenious arrangement for supplying and withdrawing it.

Ordinarily one charge of liquid will serve for twenty-four hours working, but this, of course, is entirely determined by the space provided for it. It is sold at sevenpence a gallon, and each gallon is sufficient, we are informed, to drive a cell while it generates 800 ampere hours of current, or, taking the electromotive force at 1.8 volts, it represents (800 x 1.8) / 746 = 1.93 horse-power hours. The cost of the zinc is stated to be 35 per cent. of that of the fluid, although it is difficult to see how this can be, for one horse-power requires the consumption of 895.2 grammes of zinc per hour, or 1.96 lb., and this at 18l. per ton, would cost 1.93 pence per pound, or 3.8 pence per horse-power hour. This added to 3.6 pence for the fluid, would give a total of 7.4 pence per horse-power per hour, and assuming twenty lamps of ten candle power to be fed per horse-power, the cost would be about one-third of a penny per hour per lamp.

Mr Holmes admits his statement of the consumption of zinc does not agree with what might be theoretically expected but he bases it upon the result of his experiments in the Pullman train, which place the cost at one farthing per hour per light. At the same time he does not profess that the battery can compete in the matter of cost with mechanically generated currents on a large scale, but he offers it as a convenient means of obtaining the electric light in places where a steam engine or a gas engine is inadmissible, as in a private house, and where the cost of driving a dynamo machine is raised abnormally high by reason of a special attendant having to be paid to look after it.

But he has another scheme for the reduction of the cost, to which we have not yet alluded, and of which we can say but little, as the details are not at present available for publication. The battery gives off fumes which can be condensed into a nitrogenous substance, valuable, it is stated, as a manure, while the zinc salts in the spent liquid can be recovered and returned to useful purposes. How far this is practicable it is at present impossible to say, but at any rate the idea represents a step in the right direction, and if the electricians can follow the example of the gas manufacturers and obtain a revenue from the residuals of galvanic batteries, they will greatly improve their commercial position. There is nothing impossible in the idea, and neither is it altogether novel, although the way of carrying it out may be. In 1848, Staite, one of the early enthusiasts in electric lighting, patented a series of batteries from which he proposed to recover sulphate, nitrate, and chloride of zinc, but we never heard that he obtained any success.