ESCAPEMENT FOR AN ASTRONOMICAL CLOCK. 
339 
The axis to which the arm is attached is represented in Plate XII. fig. 2. It is 
merely a piece of steel wire 3d inches long (to prevent shake), having a small plate 
of brass brazed to it at A, to which the arm is screwed. 
The piece for receiving the two axes is represented by B C, fig. 3. It is firmly 
fastened to the brass plate A, which carries the escapement, by means of screws 
passing through the piece D, which forms a part of it. The holes for receiving the 
axes are drilled quite through the ends B and C, and caps of plane brass, carrying 
planes of agate, are screwed to the ends, and keep the axes in their places, preventing 
any longitudinal motion. The axes are placed at one diameter of the scape-wheel 
above the centre. 
The pallets are of brass and faced with agate ; they are carried by arms termina- 
ting in very flexible springs, which serve merely as hinges, and these springs are at- 
tached to the arms d e and f g, Plate XI. fig. 1. ; at v and w the arms project a little 
beyond the pallets, and rest upon the screws mand n, which pass through cocks fixed 
to the arms d e and f g. The length of the arms carrying the pallets is such, that a 
tooth of the scape-wheel may rest at the bottom of the one pallet, when another tooth 
is at the summit of the opposite pallet. 
The pallets should be made light, and if it be found necessary to increase the im- 
pelling power, it may be done by fixing a pin in the arm carrying the pallet, which 
pin must pass freely through the impelling arm, and being formed with a shoulder, 
may be loaded by lodging upon it such small weights as may be necessary. 
The steel pins o and p are tapped into the arms d e and f g, and pass freely through 
holes in the arms carrying the pallets. Their position is such, as to allow of their 
acting upon the anchor at the stops q and r ; all the screws act upon small pieces of 
agate, let into the brass-work, and they are furnished with nuts to prevent any shake 
or motion after the adjustments are completed. 
The pendulum which is employed with this escapement has a glass cylinder, 
which holds the mercury used for the compensation, upon the surface of which a 
circular piece of plate glass floats, to prevent any sudden change of curvature which 
might arise from the adhesion of the mercury to the sides of the vessel, upon a change 
of temperature. This cylinder has a projecting rim at top which admits of its being 
lodged in a sort of iron hoop, formed like a box, with an aperture in the bottom 
through which the glass cylinder passes, and into which it is cemented. An iron 
cover screws into this box, having a projecting tube in the centre, to receive a glass 
tube, which is the rod of the pendulum. The pendulum is suspended by a spring in 
the usual manner, from a stout cock firmly screwed to the back of the clock-case, 
and in which all shake is precluded by the pressure of a screw passing through the 
side of the cock. 
The pendulum has a sliding weight on its rod, for the purpose of approximate ad- 
justment, and the final adjustment is effected by small weights placed upon the iron 
cover. 
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