79 
1917-18.] Studies in Clocks and Time-keeping. 
coincident with it). There are no wheels ; all the pieces move with mere 
rocking motion. The escapement is a small light cross or X, which is 
pivoted at its middle, and thrown from one side to the other by the crutch 
in its swing. The lower ends of this X are cut to a hook-shape so as to 
serve as clicks, which support the weight of an impulse piece until the 
crutch releases it by throwing the X aside. The impulse piece is a fairly 
massive piece, but with its centre of gravity close to its line of pivots so 
that in its descent it gives a firm but light blow. This blow is received by 
the edge of a small roller disc attached to the crutch. When the impulse 
piece is released, it is, as nearly as may be, at rest on the summit of this 
disc, where the latter is in its lowest position, and as the pendulum carries 
the disc aside, the impulse piece runs down the edge of the disc, doing work 
upon it. By an ingenious but simple arrangement the impulse piece then 
proceeds to release a winding piece which resets the impulse piece upon the 
click of the escapement, and then makes an electric contact which resets the 
winding piece in readiness for the next release, besides serving as a signal 
for a chronograph or for operating a counting dial ; but with this I am not 
at the moment concerned. 
