The utility of a Public Clock is considerably enhanced by its being provided with a dial marking the time in the simplest and most unmistakeable lines, so that it may readily be ascertained at any reasonable distance from the clock-tower what is the hour either by day or night. In order that this important requisite may be attained, it is of course necessary that the dial shall be so constructed as to be visible both by night and day, and so arises the necessity for providing illuminating power either from within or from without. Now the simplest method, and perhaps also in the end the least objectionable, is that followed at the Horse Guards, where the dial forms part of the tower itself, and is lighted not from within, but from without. The advantage of this arrangement is, that the architect can make the dial harmonize with the character of the building, that the illuminating power is kept apart from the clock, and if the centre of the dial be slightly sunk the hands may be brought quite close to the face, so as to prevent any seeming error in time, as is sometimes caused by the convexity of a copper dial. The figures too, having been once carefully divided and cut into the stone, are renewed, so to speak, by merely being painted over.
Memorial Turret Clock Dial.
Dials may be made of any material, wood, stone, slate, iron, brass, copper, and coloured or semi-opaque glass. Copper dials possess many advantages, and these have been of late years preferred, except where more ornamental dials are required, in which case slate and skeleton frames are used with good effect. The large dial of my great clock which was placed over the principal entrance of the International Exhibition Building in the Cromwell Road was of slate, elaborately enamelled with white and gold on a blue ground. Another kind of dial having a good effect is that erected by myself some time since for Sir Moses Montefiore, at the Synagogue, Ramsgate, consisting of a skeleton or framework of iron fitted with Minton or encaustic tiles. A dial such as this can thus be made with comparatively little expense during the erection of the tower, and the architect can then, as I have said, design it so as to be in keeping with the edifice; the Minton tiles have also the advantage of being almost indestructible, and of being made of any pattern or colour. The chief points to remember are that the dials should be slightly sunk in the centre so as to allow the hour hand to traverse in the sinking point close to the disc and the figures, and especially that the dial should be made large enough to distinctly show the hour. Properly the dial should never be less in diameter than one-tenth of the number of feet which it is distant from the ground, and in all cases where it is possible I should recommend it to be much larger than this. The dials of St Paul's and Westminster are larger than they would be under the above rule, and they are certainly not too large. As to the colour of the dials, figures, and hands, there is not much choice; dark ground and gilt figures, or white ground with black figures, or a skeleton frame with gilt figures are the chief in use. In the white semi-transparent dials with opaque figures used for illuminated clocks, the time, which is seen with sufficient distinctness by night when the light is behind the figures, is not as clearly indicated by day. To remedy this defect an invention has been applied by which the dial when illuminated at night throws out a beautiful transparent light admirably marking the position of the figures and hands, which being black or dark blue, or even strongly gilt, can also be distinctly seen by day, even as clearly as the long-approved copper dials painted black with gilt figures.
THE HANDS
should be most carefully made, and like the figures should be painted of a colour which shall most powerfully contrast with that of the dial. The hands are almost invariably made of copper strengthened by diaphragms, and poised from the inside. In some old-fashioned clocks in which the hands have been poised from the outside the effect has been produced of a third hand, and numerous mistakes caused thereby. As to the shape of the hands, there is but one simple rule, namely, that the less of ornamentation in them the better. The minute hand should be perfectly plain, with a tapering but not too fine point, extending to the top of the figures; the hour hand should be of equal breadth and plainness, but its point should be more marked by perhaps an arrowhead or heart-shaped tip only reaching to the bottom of the figures. With large hands counterpoises are found necessary, and these should be placed inside the dial if possible, for they are when outside sometimes mistaken for the point of the hour hand. If a counterpoise must be placed outside, it is better to arrange that it shall be as little as possible, and that the inside counterpoise make up the difference, giving to the latter perhaps two thirds, and one third to the former,—but in any case care has to be taken to prevent the counterpoise appearing like a hand.
THE FRAME.
The old-fashioned clock-frame, known in the trade as the 'bedstead,' is now generally superseded by the horizontal frame originally introduced by the French, which possesses the special advantage of not only being durable and strong, but that it allows of any part of the clock which may have been injured, or may require cleaning, being easily taken out and replaced without interfering with other portions of the mechanism,—any wheel can be separately handled and removed. In the old upright frame which is even now still in use by some of the more ancient firms of clockmakers, if any part of the clock be injured the entire machine must be taken to pieces.
THE FIXING
of a Turret Clock requires much careful forethought and experienced labour; because whatever oversight has been made by the architect in planning the clock-room must be made good by the clockmaker who has to fix up a public time-piece. In the first place the latter will take care that the supports of the clock shall be sufficiently strong and free from vibration, and that the movement shall be bolted securely to the iron girders, or strong oak beams provided for the purpose; he will remember that when it is intended that the clock shall strike the hours and quarters, that the bell or bells should be hung as high in the tower as possible, so that when the stroke of the hammer is given by a perfect fall of the weights, the louvres of the tower should be so arranged as to bring out the full sound of the bell, as in the case of the bell at St Paul's cathedral, which, though only weighing 5 tons 4 cwts., is frequently heard on clear nights as far as Windsor. He will in a word require to be acquainted with all the points of importance attached to his rather intricate duty, or he may by failure render nugatory the best workmanship that could be bestowed in clockmaking. The wiser arrangement as to clock-fixing is to intrust the duty to the clockmaker, and he will then necessarily bear the sole responsibility of any mistake.