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 110_l._, 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]