These automata remind us of the Minute-Jacks in Shakspeare’s _Timon of Athens_, generally interpreted as Jacks of the Clock-house: You fools of fortune, trencher friends, time’s flies, 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.