The regulator adopted is the vibrating pendulum, because amongst the means at the mechanician’s command for obtaining perfect time-keeping there is none other by which the same degree of accuracy can be obtained. The difficulty in this construction is the conversion of the jerking or intermittent motion produced by such pendulums into a uniform rotatory motion which can be available with little or no disturbing influence on the pendulum itself, when the machine is subject to varying frictions and forces to be overcome in driving large equatorials. The pendulum is a half-second one, with a heavy bob, adjusted by sliding the suspension through a fixed slit. It is drawn up and let down by a lever and screw, the acting length of the pendulum being thus regulated. The arrangement of the wheels represents something like the letter U. At the upper end of one branch is the scape-wheel. At the upper end of the other branch is an air-fan. The large driving-wheel and barrel are situated at the bottom or bend. All the wheels are geared together in one continuous train, which consists of eight wheels and as many pinions. The scape-wheel and the two following wheels have an intermittent motion; all the others have a continuous and uniform one. The change from one motion to the other is made at the third wheel, which, instead of having its pivot at the end of the arbor where the wheel is fixed—fixed to the frame like the others—is suspended from above by a long arm having a small motion on a pin fixed to the frame; the pivot at the other end of the arbor is fixed to the frame as the others are, but its bole and its pivot are arranged so as to permit a very small horizontal angular motion round them, as a centre, without interfering with the action of the gearing of the wheel itself. If the weight is applied to the clock, and the pendulum is made to vibrate, the moment it begins to move, the scape-wheel moves its quantity for a beat; the remontoire wheel, by the very small force outwardly caused by the reaction of the break-spring, relaxes its pressure against a friction-wheel, and sets at liberty the train of the clock. The spring is now driven back to the break-wheel, but before it can produce more than the necessary friction to keep the train in uniform motion, another beat of the clock again releases it. The repetition of these actions produces a series of impulses on the break-wheel of such a force and nature as to keep the train freely governed by the pendulum. The uniform rotatory motion obtained by this clock as far as experiments can be made by applying widely different weights, and comparing the times with a chronometer, is perfectly satisfactory. A clock constructed on the same principle, connected, and giving motion to a cylinder, will, it is presumed, make an excellent chronograph. [Illustration: FIG. 148.—Foucault’s governor. ]