^00 M. Van Swinden m the Invention of Pendulum-Clocks 
superintendence, {Leyden MSS.)^ ; and astronomers from thence 
began to relinquish their former balance apparatus, which was 
soon entirely superseded by the pendulum clock. 
Notwithstanding the important discovery thus made, it was 
to be expected, at a time when the application of mathema- 
tical theories to mechanics was far from being generally un- 
derstood, that the principle of the new contrivance, namely, 
the reciprocal action of the wheels and pendulum on each other, 
(the latter regulating the former, whilst it is prevented by them 
from returning to rest,) would not be immediately and fully 
comprehended by all, but give rise to several objections. We 
must therefore enter into a more particular detail of the uses 
and construction of the balances, for which the pendulum came 
to be substituted, in order to show how greatly the old principle 
fell short of the new, in answering the end of a proper regula- 
tor of the work, confining our attention to that part of clock- 
work to which the invention more immediately belonged, and 
which is called the Escapement 
The old works, then, may in this respect be reduced to two 
classes. In the first, Fig. 3. Plate VII. the balance TT was 
supported on a perpendicular arbor MN, the pallets M and N 
of which acted on the teeth of an upright crown or balance- 
wheel LL. When Huygens substituted the pendulum, he only 
at first altered this arrangement, in so far that he fixed on the 
perpendicular arbor MN, Fig. 1. a pinion, or smaller wheel O, 
which not having a revolving but swinging motion, as well as 
the arbor itself, engaged by its leaves the teeth of a larger wheel 
P, supported on the horizontal part of the bent wire TQR, 
which transmitted the reciprocal actions of the pendulum and 
clockwork. , By this contrivance, and because the diameter of 
the wheel P was double or treble of that of the pinion O, Huy- 
gens judged that small vibrations of the pendulum would keep 
the clock going, and that small irregularities in its motion could 
not disturb the uniform rate or isochronism of the workf, — an ex- 
• Among these are letters of Mylon and Bouillan, distinguished mathemati- 
cians at Paris, Wallis, Jacquet, Gregorius a Sancto Vincentio, Kinner of Vienna, 
Slusius, and Pascal, 
•j- Horologium^ p. 12 Fig. 1. is taken from the diagram affijted to the Horo- 
logium ; only those parts are omitted which do not immediately concern the escape- 
