418 Proceedmgs of the 



bead describe exactly the same lines, though upon different planes. 

 Thus a drawing is made without ever looking at the paper, but 

 solely at the object. 



The meetings, having been suspended during Passion and Easter 

 weeks, were again resumed on the evening of Friday, 



April ISth, 

 when Mr. Ainger described and illustrated the various escape- 

 ments for timekeepers. 



His object, he said, was to explain, by means of very enlarged 

 models, the principles and action of those ingenious and beautiful 

 contrivances which are generally little understood, because of the 

 minuteness of their parts and the rapidity of their motions, which 

 render their mode of operation in machines of the ordinary size too 

 obscure and transient to be understood by mere inspection. To ob- 

 viate this difficulty, a model was made three feet in diameter, of the 

 wheel called the escape wheel, which in coinmon clocks is not a$ 

 many inches in diameter, and in watches is of course much less. 

 This model, with its appendages, was made to move with a propor^ 

 tionate degree of slowness, so that the action and reaction of the 

 parts became obvious and intelligible. 



A timekeeper may be divided into two parts : 



1. The motive part, 



2. The regulating part. - 



The first merely produces motion, the second regulates its velocity. 

 The motive part may be subdivided into 



(1) The motive power, which is a weight or spring. 



(2) The distributive power, which is a train of wheels increasing 

 the velocity, and of course diminishing the intensity of the force 

 arising from the descent of the weight, or the uncoiling of the spring. 



The use of the train of wheels will be understood by considering 

 that the weight or spring barrel of a thirty day clock, will not make, 

 perhaps, more than ten revolutions, while the second's hand of th^ 

 same clock will, in the same time, make fifty thousand revolutions. 

 The train of wheels, therefore, multiplies the insensible velocity ge- 

 nerated by the weight or spring, till it becomes the visible velocity 

 of the second's hand, which is placed on the axis of the last wheel 

 of the train called the escape wheel ; this wheel has, therefore, a con- 

 stant tendency to move in obedience to the impulse communicated 

 through the train from the weight or spring. This tendency to move 

 is what keeps the clock going ; but the motion requires to be regu- 

 lated, and made perfectly uniform, which leads to a consideration of 

 the other essential part of a timekeeper, the regulating part. 



