338 
MR. KATER’S DESCRIPTION OF CAPTAIN RATER’S 
unlocking- the detent. To calculate with accuracy the time the arm is detained is 
perhaps impossible, but a sufficient approximation to this may, and has been made, 
to demonstrate that it cannot overtake the pendulum during the unlocking of the 
scape-wheel, which is all that is necessary. 
This escapement, therefore, is demonstrably one of equal impulse, the impelling 
power being purely the pressure of the pallet in its descent, through a space equal to 
the height of its inclined plane. 
I shall now give the directions which my father considered might be necessary for 
the construction of the escapement. 
The various parts which compose the escapement are attached to a piece of plate 
brass, which is afterwards screwed to the back plate of the clock, in such a position 
as to place the detents in their proper situation with respect to the scape-wheel. The 
anchor, as already mentioned, 0'24 inch thick, and weighing 403 T4 grains, is 
made thus heavy in order that its inertia may be sufficient to arrest the descent of 
the impelling arm, so that, during the raising of the detent, the arm cannot possibly 
overtake the pendulum. The form of the anchor is sufficiently indicated by the plate. 
The axis is of steel, and turned with shoulders : it is made to pass through the 
centre of gravity of the anchor by filing it away when necessary, after the detents 
are attached to it. The detents are small plates of agate, properly bevelled at the 
extremity, and fixed in their places by shell-lac. The distance between the faces 
comprise eight and a half teeth of the scape-wheel, and the chord or distance between 
the extremities of the detents may be found by multiplying the diameter of the 
scape-wheel by 0 '777- If lines y a and y b be drawn from the axis of the anchor 
to the extremity of each detent, and the faces of the detents be produced to a! and b', 
the angle y bb' should be rather less, and the angle y a a' should be rather more 
than a right angle ; perhaps a difference of five degrees from a right angle may be 
quite sufficient. The object in this is to give a tendency to the scape-wheel to draw 
the detents downwards. 
The anchor is screwed in its place by means of a cock, which receives one end of 
the axis, the other end passing into the brass plate. 
The distance of the axis of the anchor above the centre of the scape-wheel is 
found by multiplying the diameter of the scape-wheel by 0-64. 
The steel stops, q and r, are rivetted into the brass plate, but not so firmly but that 
they may be turned by a screw-driver. The upper part of these stops is made either 
oval or eccentric. They serve to regulate the depth to which the detents are to 
engage the teeth of the scape-wheel. 
The arms d e and f g are of plate brass. The length of each arm, from the point 
where it is attached to the axis, in a straight line drawn to the lower end where 
the steel wire projects, is about 4’8 inches. Each of these arms is attached to an j 
axis by a screw and steady pin, and from the lower end of each arm, a piece of steel 
wire projects for the purpose of impelling the pendulum. 
