ESCAPEMENT FOR AN ASTRONOMICAL CLOCK. 
337 
them down from his own dictation, and frequently assisted him in many of the ex- 
periments, I can give this description as if it came from his own pen. I have added 
also a more minute account of its various parts, and of their size and weight, which 
I have lately estimated. 
In Plate XI. fig. 1., A represents a piece of brass, which is called from its shape the 
anchor, to which the detents, a and b, made of thin plates of agate, are attached. 
The anchor is supported on an axis passing through its centre of gravity : it is 0*24 
inches thick, and weighs about 4031*4 grains. The detents are regulated so as to 
engage at the proper depth by means of the pins q, r, having oval or eccentric heads. 
Two arms, d e and f g, are supported by two separate axes at d and f; and at e and g , 
two steel pins project at right angles to the arms, between which is the cross-piece of the 
pendulum, upon which these steel pins act. Two pallets, h and i, faced with agate, are 
attached to the arms k v, l , w, and move by the flexibility of their springs at 
t and x, which serve merely as joints. The motion of the pallets is limited and re- 
gulated by the screws m and n, which pass through cocks attached to the arms d e 
and f g. Two screws, o and p, are tapped into the arms d e and f g, and pass 
through large holes made in the arms carrying the pallets. These screws are intended 
to act upon the anchor, and raise the detents. 
Fig. 1. represents the situation of the different parts of the escapement when the 
pendulum is descending in the direction indicated by the arrow. On the one side, a 
tooth of the scape-wheel having elevated the pallet i through a space equal to the 
height of its inclined plane, is resting on its summit. The anchor is pressed upon 
by the screw p, with the weight of the arm f g, so as to render any tripping im- 
possible, and the scape-wheel is locked by the detent a. As the pendulum advances, 
the cross-piece meets the projecting wire at g, carries forward the arm f g, frees the 
anchor from the pressure of the screw p, leaving it free to be acted upon on the 
other side, and ultimately raises the pallet i, by means of the screw n meeting its 
arm. By the time this has been effected, the bottom of the inclined plane of the 
pallet h meets a tooth, and the screw o is all but in contact with the anchor. The 
weight of the pallet h is thus taken off from the pendulum, whilst the weight of the 
arm d e continues for a moment to impel it, till the screw comes in contact with the 
anchor. At this instant a sudden stop, during a small fraction of a second, takes 
place in the motion of the arm, in consequence of the vis inertise arising from the 
great weight of the anchor. The pendulum, therefore, is no longer rested upon, but 
having quitted the wire at e, the weight of the arm d e overcomes the inertia of the 
anchor, the detent b is pressed down, and the scape-wheel being freed, raises the 
pallet h , and rests on the summit by another tooth having come in contact with the 
detent b. 
Such is the action of this escapement. Its perfection depends on the action of the 
arm upon the pendulum being at once checked, and terminated by the vis inertiae 
of the anchor, in which case the pendulum quits it, leaving to the arm the work of 
mdcccxl. 2 x 
