One object of great convenience and utility to which gas lighting has within these few years been applied, is the illumination of public clocks. This we believe was first put in practice at Glasgow, where a clock with two faces, supported at the extremity of a projecting bracket, was lighted by jets placed above it, the light of which was reflected on each face from mirrors placed within the wings of an elegant representation of a phoenix, which sur mounted the clock. In order to light the burner without sending up a per son for that purpose, in addition to the pipe which supplied it with gas, was another extending from the main to the burner, having a stop-cock at its junction with the main, and being perforated with numerous small holes throughout its length. Upon opening the cocks, the gas flowed through both pipes, and issued at the small holes in the flash pipe as it was called ; and a light being applied below, quickly communicated along the whole length of the flash-pipe, and upon reaching the jet, ignited the gas issuing from it; after which, the cock on the flash pipe was shut. Various methods have since been proposed of lighting up clocks, one of which is as follows : a dial plate, out of which the figures representing the hours are cut, in contrary succession to the usual representation of them, is made to revolve on the axis that would other wise receive the hour hand. Behind it is a solid field, out of which a sufficient space is cut to show the hour, half hour, or quarter ; each half hour is repre sented by a star, and each quarter by a dot; and the time is reckoned by the hours and quarters which have passed the centre of the opening Behind the revolving plate is placed a gas light, which is ignited by the jet of gas being directed on to a piece of spongy platina.
A somewhat superior method to the preceding is exhibited in the following engraving. A is the dial plate of a common clock, with the hours, &c. marked upon it, as usual; B is the proposed addition to it, for the purpose of exhibiting the time distinctly during the night ; C is a light cog-wheel, placed immediately behind the day dial; having its centre fitted in the arbour of the hour hand, and revolving with it. The night dial B is designed to be made of plate glass, with the hours painted upon it in black, and to revolve on an axis in its centre. The index represented by an arrow is fixed. The periphery of the glass plate is encompassed by a rim of brass, having cogs in its outer edge, which fits into the cogs of the wheel C ; consequently they move together, and being of equal diameters, they perform their revolutions in equal time. The time represented in our engraving, is a quarter past X ; when the hour hand has moved on to XI. (for instance), the transparent dial B will have moved an equal space past the fixed index, and denote the same precise time. Both dials must, by this simple contrivance, invariably agree in their respective indi cations of the time. During the day, the time is observed on the large dial as usual ; and at night a lighted lamp placed behind the transparent dial will always exhibit the time as distinctly.
But the most perfect and ingenious mode of illuminating public clocks which has come under our notice, is that by which several of the church clocks in London are lighted. By the revolution of the hands, and the addition of only one wheel and pinion to the clock, the gas is lighted and extinguished at regular stated hours, which hours may be varied monthly to suit the increase or decrease in the length of daylight, by simply adding or withdrawing a pin. The inventor is Mr. Paine, from whose account in the Transactions of the Society of Arts we have taken the following abbreviated description.
Reference to the Engraving.—Fig. I represedts a skeleton frame dial, cast all in one piece ; the eight central divisions are very thin, and curved, so as not to coincide or interfere with the hands while passing over them ; the spaces are all filled up with transparent red glass, ground rough on the inside. This by day is sufficiently dark to relieve and render distinctly visible the gilt hour numbers; but at night, when the gas burners behind the dial plate are lighted up, the hours, minutes, and bands appear black, and the rest of the dial glows with a dusky red light. Fig. 2 is a horizontal section across the aperture a a in the church tower at the back of the dial b b; c the tube which carries the hour hand, having a balance weight and the wheel 48 on its inner end ; through this passes the shaft d d, holding at one end the minute hand, and at the other end the pinion 14 and balance weight e ; f f two gas burners; g g the tubes supplying the gas; the aperture a a, not being so large as the dial, is cham ferred off at i i, to give a clear passage from the lights all over the dial ; j j a curved reflector, made of sheets of tin; k k a bar crossing the aperture a a within, to support the motion wheels, and the additional twenty-four-hour wheel, 96; the long axis d d receives motion from the clock (as usual) by a bevel wheel; 14, 42, 12, and 48, Fig. 3, are the usual motion wheels and pinions; an additional pinion of 12 is put on the wheel 42, to turn the wheel 96; this has thirteen pins, one hour's motion apart ; these pins raise up the weighted lever 1, in Fig. 3, and let it drop; while this is up, (as shown by the dotted lines,) its opposite end by means of the connecting rod a, keeps the lever handle o of the gas cock p down, and thus nearly closes it, allowing the passage of only just enough gas to keep the burners alight; but at eight o'clock, when the weight 1 drops, it raises the handle o and quite opens the cock p, by which the dial is instantly illuminated. Thus, Fig. 3 represents the lever 1 down, and the pins nearly beginning to raise it; by removing two pins, one at each end, the clock will open the gas-cock one hour sooner, and nearly close it one hour later. By successively removing the pins as the days shorten, and replacing them as the days lengthen, the clock is accommodated to all seasons. The whole space is kept clear between the lights and the dial, except only the axis e, lig. 2 ; and the lights being placed on each side of this, and having a large reflector, no shadow is perceived finm it.