Notwithstanding the application of the pendulum, and the ingenious connivance of cycloidal checks by Huygens, in order to make the long and short vibrations be performed in nearly as equal time as possible, yet the clock did not keep time with that correctness which was expected: This arose from the great extent of the arc of vibration, the lightness of the pendulum ball, the great dominion which the clock had over the pendulum, and the bad effects pro duced by the cycloidal cheeks, which, however excellent in theory, were never found useful in practice. See Plate CCC. Fig. 4. where a front view of the cycloidal cheeks is represented in Fig. A. This led artists and amateurs of the profession to think of farther means of improvement ; accordingly, about the year 1630, a clock was made by W. Clement, a clock-maker in Loudon, having, in place of the crow wheel and verge 'scapement, a 'scapement which was nearly the same as the common recoiling 'scapement of the present day. The swing-wheel, S W, was flat, having a sort of racket or saw-like teeth : and the pallets, P P, had remote resemblance to the head of an anchor, by which it ac quired at that time the name of the anchor 'sediment. See Fig. 5. The ball of the pendulum was made much heavier than what had formerly been adopted, the arc of vibration much shorter, and the motive force much less. From the excellent time-keeping of the clock, this was found to be a great improvement, and hence this 'scapement was af terwards generally practised. • It passed into Holland and Germany, and was hardly known in France until the year 1695. See Histoire de la Mesure du Temps, torn. i. p. 100.
At the time when this clock of Clement's appeared, Dr Hooke claimed the invention of it as his, and affirmed, that after the great lire of London, in 1666, he had shewn to the Royal Society a clock with this very 'scapement. 44 Con sidering," say s Sully, in his Histoice des Echappernene," the genius, and the great number of fine discoveries of this excellent man, I sec no room to doubt that he was the first inventor of it." The pendulum with this 'scapcment had received the name of the royal pendulum.
'l'hc dead•beat 'scapement of Graham's next succeeded, which was invented some time after the beginning of the eighteenth century, and has continued to be that which is generally used in regulators, or astronomical clocks, with a very few exceptions. Sec Fig. 6. About ten or fifteen years afterwards, it came to be known in France, and was adopted there also, as the best for clocks intended to mea sure time very accurately. Lepaute, a very ingenious watchmaker in Paris, produced, about the year 1753, or some time before it, a 'scapement founded on that of G ra hem's dead-beat one. See Fig. 7. In Lepautc's, the rest of the teeth on the pallets was always with the same effect, because it was on the same circle, whichever of the pallets it rested upon ; the impulse given was also always the same on whichever pallet it was given, the Hunches of the pallets being planes equally inclined. This was 110 doubt some improvement on Graham's; but the teeth of the swing wheel it, Lepaute's coasisted of sixty small pins, thirty being arrang ed on each side of the rim of the wheel ; and where pin-teeth are used, oil, which is in some degree necessary, cannot easi ly be kept to them, the attraction of the rim of the avheel constantly draining the oil from these pin sort of teeth ; an evil which is perhaps not easily to be got the better or, un less by using stone pallets and hard tempered steel pins.
Notwithstanding the seeming superiority and great cha racter which the dead beat 'scapement had long acquired over that of the recoiling one represented in Plate CCC. Fig. 8. this last had, however, its partizans; and among them were artists and amateurs possessed of first rate talents. Stich were Harrison, Professor Ludlam of Cambridge, Berthoud, Smeaton, and others. Harrison, indeed, always rejected the dead beat 'scapement with a sort of indigna tion. The author of the Elements of Clock and Watch Making, has said a great deal in favour of the dead beat, and as much against that of the recoiling one, without hav ing shown in what the difference consisted, or what was the cause of the good properties in the one, or w hat the defects in the other. It appears doubtful if these causes were known to him ; yet he was very deservedly allowed to be a man of considerable genius. When pallets are intended to give a small recoil, their form, it' properly made, differs very lit tle front those made for the dead beat, as may be seen by the dotted lines upon the dead beat pallets in Fig. 6.
We shall endeavour to point out the properties and de fects naturally inherent in each : When the teeth of the swing wheel, in the recoiling 'scapcment, drop or fall on either of the pallets, the pallets, from their form, make all the wheels have a retrograde motion, opposing at the same time the pendulum in its ascent, and the descent, from the same cause, being equally promoted. This recoil, or retro grade motion of the wheels, which is imposed on them by the reaction of the pendulum, is sometimes nearly a third, some times nearly a half or more of the step previously advanc ed by the movement. This is pet baps the greatest, or the only defect that can properly be imputed to the recoiling 'scapement,and is the cause of the greater wearing in the holes pivots, and pinions, than that which takes place in a clock or watch having the dead beat, or cylindrical 'scapement ; but this defect may be partly removed by making the recoil small, or a little more than merelyia dead beat. After a recoiling clock has been brought to time, any additional motive force that is put to it will not greatly increase the arc of vibration, yet the clock will be found to go considerably faster ; and it is known that where the arc of vibration is increased, the clock ought to go slower, as would be the case, in some small degree, with the simple pendulum. The form of the recoiling pallets tends to accelerate and multiply the num ber of vibrations, according to the increase of motive force impressed upon them, and hence the clock will gain on the time to which it was-before regulated. Professor Ludlam, who had four clocks in his house, three of them with the dead beat, and the other with a recoil, said, " that none of them kept time, fair or foul, like the last : This kind of 'scapement gauges the pendulum ; the dead beat leaves it at liberty." Were it necessary, many good proofs could be adduced of the excellent performance of clocks which had the recoiling 'scapement.