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XVII. Description of an Escapement for an Astronomical Clock, invented by the late 
Captain Henry Kater, F.R.S. fyc., drawn up from his own Memorandums by his 
Son Edward Kater, Esq. Communicated by Sir J. F. W. Herschel, Bart., 
K.H. F.P.R.S. %c. 
Received March 26, — Read April 30, 1840. 
In venturing to offer to the attention of the Royal Society the following description 
of an escapement for an astronomical clock, I beg to premise that I restrict myself 
almost entirely to the collecting and arranging of my father’s own notes respecting 
it, written at intervals during the many years he was engaged upon it. His last im- 
provement was made very shortly before his death, but from increasing ill health he 
was unable to pursue the requisite observations for verifying the accuracy of the pre- 
sent plan. 
Owing to the numerous memorandums left by my father on this subject, I am for- 
tunately able to give the description of the escapement nearly in his own words, with 
but little addition beyond some drawings which I have made to elucidate the expla- 
nations. 
I regret that I have not had an opportunity of trying this escapement myself, but 
from the great care and attention which my father bestowed upon it, I am induced to 
believe that it may prove a valuable invention. 
The two escapements most usually found in observatories, viz. Graham’s dead beat 
and Mudge’s escapement, were objected to by my father, on the ground of the fatal 
defect common to them as well as to all others hitherto invented, namely, that the 
impulse communicated to the pendulum is affected by any irregularity with which the 
impelling power is transmitted through the train. 
If the number of wheels and pinions of which the train consists be taken into con- 
sideration, it was his opinion, that no excellence of workmanship can ever ensure that 
equality of ultimate action on the pendulum, which is the great desideratum, and 
which is necessary to its perfect performance. 
In the dead beat escapement, the impulse is given by the teeth of the scape-wheel, 
pressing and sliding on inclined planes or pallets connected with the pendulum, 
which thus urges it in the direction of its vibration. The degree of impulse, there- 
fore, communicated to the pendulum, will depend on the force with which the teeth 
of the scape-wheel press upon the inclined planes, and this will vary according as 
the moving power is transmitted with more or less freedom through the train. 
Mudge’s escapement consists of two arms, moving on separate axes, and terminated 
