WATCH-WORK.

OUR intention in this article does not extend to the manual practice of this art, nor even to all the parts of the machine. We mean to consider the most important and difficult part of the construction, namely, the method of applying the maintaining power of the wheels to the regulator of the motion, so as not to hurt its power of regulation.

The regulator of a clock or watch is a pendulum or a balance. Without this check to the motion of the wheels, impelled by a weight or a spring, the machine would rum down with a motion rapidly accelerating, till friction and the resistance of the air induced a sort of uniformity, as they do in a kitchen jack. But if a pendulum be so put in the way of this motion, that only one tooth of a wheel can pass it at each vibration, the revolution of the wheels will depend on the vibration of the pendulum. This has long been observed to have a certain constancy, insomuch that the astronomers of the East employed pendulums in measuring the times of their observations, patiently counting their vibra

tions during the phases of an eclipse or the transits of the stars, and renewing them by a little push with the finger when they became too small. Gassendi, Riccioli, and others, in more recent times, followed this example. The celebrated physician Sanctorius is the first person who is mentioned as having applied them as regulators of clock movements. Machines, however, called clocks, with a train of toothed wheels leading round an index of hours, had been contrived long before. The earliest of which we have any account is that of Richard of Wallingford, Abbot of St. Alban's, in 1326 *. It appears to have been regulated by a fly like a kitchen jack. Not long after this Giacomo Dondi made one at Padau, which had a motus succussorius, a hob bling or trotting motion; from which expression it seems probable that it was regulated by some alternate movement. We cannot think that this was a pendulum, because, once it was introduced, it never could have been supplanted by a balance. The alternate motion of a pendulum, and its seeming uniformity, are among the most familiar observations of common life; and it is surprising that they were not more early thought of for regulating time measurers. The alternate motion of the old balance is one of the most far-fetched means that can be imagined, and might pass for the invention of a very reflecting mind, while a pendulum only requires to be drawn aside from the plumb-line, to make it vibrate with regularity. The balance must be put in motion by the clock, and that motion must be stopped, and the contrary motion induced; and we must know that the same force and the same checks will produce uniform oscillations. All this must be previously known before

Professor Beckmann, in the first volume of his History of Inventions, expresses a belief that clocks of this kind were used in some monasteries so early as the 11th century, and that they were derived to the monks from the Sara. His authorities, however, are discordant, and seem not completely sa tisfactory even to himself.

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