III. On the Disturbances of Pendulums and Balances, 

 and on the Theory of Kscapements. 



By GEORGE BIDDELL AIRY, MA. 



PLUMIAN PROFESSOR OF ASTRONOMY AND EXPERIMENTAL PHILOSOPHY, FELLOW OF TRINITY 

 COLLEGE, AND OF THE CAMBRIDGE PHILOSOPHICAL SOCIETY. 



[Read Kov. 26, 1826.] 



Having lately had occasion to investigate the disturbance 

 produced in the motion of a pendulum by a small external force, 

 and having found by a very general investigation a result of 

 great simplicity, I perceived that the usual theorems for the 

 alteration in the time and extent of vibration produced by the 

 difference between cycloidal and circular arcs, by the resistance 

 of the air, by the friction at the point of suspension, &c. could 

 be made to depend on it ; and that these alterations could in 

 fact be found with greater facility from this general theorem 

 than from the independent and unconnected inve.stigations. I 

 found also that the same principles could be applied with great 

 ease to that important practical subject, the escapements of 

 clocks — a subject upon which I believe no distinct theory has 

 ever yet been laid down. The investigations which have been 

 the fruit of these considerations are now presented to the notice 

 of this Society : the theory of escapements is by no means com- 

 plete, but I hope it will be found that the principal points 

 have been touched on, and that enough is .said to enable any 

 one else to pursue the subject as far as he may wish. 



Vol. in. Vart I. O 



