Cap and knee slaves, vapours, and minute-jacks.
Still, the Minute-Jacks only struck hours and quarters; and the term is rather thought to mean “fellows that watch their minutes to make their advantage, time-servers.” There is no doubt that by the “Jack that keeps the stroke,” in Richard III., is meant the Jack of the Clock-house.[[15]]
A much more noteworthy sight than the Fleet-street clock-figures is possessed by the Londoners of the present day in the Time-ball Signal upon the roof of the Electric Telegraph Office, No. 448 West Strand.
The signal consists of a zinc ball, 6 feet in diameter, supported by a rod, which passes down the centre of a column, and carries at the base a piston, which, in its descent, plunges into a cast-iron air-cylinder; the escape of the air being regulated so as at pleasure to check the momentum of the ball, and prevent concussion. The raising of the ball, half-mast high, takes place daily at 10 minutes to 1 o’clock; at 5 minutes to 1 it is raised to the full height; and at 1 precisely, and simultaneously with the fall of the Time-ball at Greenwich Observatory (by which navigators correct their chronometers), it is liberated by the galvanic current sent from the Observatory, through a wire laid for that purpose. The same galvanic current which liberates the Ball in the Strand moves a needle upon the transit-clock of the Observatory, the time occupied by the transition being about 1-3000th part of a second; and by the unloosing of the machinery which supports the ball, less than one-fifth part of a second. The true moment of one o’clock is therefore indicated by the first appearance of the line of light between the dark cross over the ball and the body of the ball itself. There is a similar Time-ball upon the roof of a clockmaker’s in Cornhill.
At Edinburgh, also, is a Time-ball connected with a Time-gun signal, consisting of a large iron cannon, in the Half-moon Battery, at the Castle; which cannon, having been duly loaded and primed some time between twelve and one o’clock, is fired off precisely at the latter hour by an electric influence from the corrected Mean-time of the Royal Observatory, at a distance of three-quarters of a mile; which, however, first passes to another clock close to the gun, and thus affords a short fraction of a second before one o’clock for the train of processes; so that the actual final flash of the exploding gun in the Castle occurs absolutely coincidently with the tick of the sixtieth second of the corrected mean-time clock in the Royal Observatory. The whole is well described by Professor Piazzi Smith, Astronomer-Royal for Scotland, in Good Words, 1862, part iv.
We now return to the details of the great London Clocks. Mr. Dent undertook the construction of the Royal Exchange Clock in 1843: it was required to be superior to any public clock in England, and to satisfy certain conditions proposed for the first time by the Astronomer-Royal, and such as could not be satisfied by any clock of the common construction. Mr. Dent had then no factory of his own for making large clocks, and he could not get the clock made for him; “but with the energy and genius by which that remarkable man raised himself from a tallow-chandler’s apprentice to the position of the first horologist in the world, he set up a factory for himself at a great expense, and made the clock there; and of this, the first turret-clock he had ever made, the Astronomer-Royal certified, in 1845, that it not only satisfied his conditions, but that Mr. Dent had made some judicious improvements upon his suggestions, and that he had no doubt it was the best public clock in the world.”[[16]] It is true to a second of time, and has a compensation-pendulum.
The Westminster Palace Clock, designed by Mr. Denison, has four dials, each 22½ feet wide: they are not the largest in the world, being considerably less than the dial at Mechlin; but there is no other clock in the world which has to work four dials of such great width, especially a clock going 8½ days. St. Paul’s Clock has only two 17-feet dials, and is wound up every day, which makes a vast difference in the power and strength required. Each pair of hands weighs above 2 cwt.: they are made of gun-metal, instead of sheet-iron or copper. The hour-sockets are iron tubes, 5 inches in diameter; the dials are of cast-iron framework, filled with opal glass, and stand out 5 feet from the main walls.
The size of public dials is often very inadequate to their height, and the distance at which they are intended to be seen. They ought to be at least one foot in diameter for every ten feet of height above the ground, and in many cases more, whenever the dial will be seen far off. Now, the clock-dials of St. Pancras, Euston-square, are but 6½ feet in diameter, though at the height of 100 feet, and therefore are much too small.
The Clock, of silver-gilt, presented by Henry VIII. to Anne Boleyn on the morning of their marriage, is one of the earliest chamber-clocks in the kingdom: the case is richly chased and engraved, and on the weights are the initial letters of Henry and Anne, with true-lovers’ knots. This clock was purchased at the Strawberry Hill sale in the year 1842, for 110l., and is now in the collection of Queen Victoria.
We may here mention that the late Duke of Sussex possessed, at Kensington Palace, an invaluable collection of the early as well as the most perfect specimens of Time-keepers, among which was “Harrison’s first Clock, the forerunner of that invaluable machine, without which the compass itself would be but an imperfect guide to the mariner.”[[17]]