218 Mb AIRY ON A NEW CONSTRUCTION OF THE GOING-FUSEE. 



flexible and elastic to expand without great diminution of that force 

 through a sensible space. There is doubtless no difficulty in satisfying 

 these conditions in the case of a coach-spring, or where there is abundance 

 of room : but, where the spring must be contained within not a clock 

 but a clock-wheel, there is considerable difficulty. The only way in which 

 I could hope to use the principle, must be by adopting a barrel, ratchet, 

 click, and first wheel, exactly as in a kitchen - clock ; and removing the 

 ratchet-wheel of Harrison's fusee with its click and going-spring to the 

 spindle of the next wheel, where the forces are much diminished. But 

 here it would be necessary to use a spring which is coiled several times 

 round the spindle ; else, as this second wheel revolves more rapidly than 

 the first, the spring would be too much relaxed before the cessation of the 

 pressure of the hand allowed the weight to act again. The difficulty of 

 manufacturing the spring would be great, and in all contrivances re- 

 quiring a steel spring there was the risk of rust, against which I could not 

 hope to secure the machinery. 



I might have adopted the contrivance known as the endless cord of 

 Huyghens, which has been employed in Fraunhofer's clocks. The only 

 objection to the use of this construction for the Northumberland clock 

 was, that the spikes in the gorge of the pulley, which are necessary to 

 prevent the cord from slipping, would speedily have torn the cord to 

 pieces, when a weight of 100 lb. was attached. 



Abandoning the spring and the endless rope, my first idea was, to 

 use a new weight in such a manner as to produce exactly the same effect 

 and in the same place as Harrison's going-spring. Various constructions 

 presented themselves ; but those founded on the following principle, ap- 

 peared the most feasible : — The action of a spring may be exactly imitated 

 by that of a jointed lozenge : the two parts which are to be connected 

 by the spring being two opposite angles of the lozenge, and the two 

 other angles being pulled apart by the action of constant weights. In 

 the application of this principle, the parts to be connected by the spring 

 or lozenge would be on the circumference of the barrel and wheel, and 

 the two other angles would therefore be on the same circumference : but 

 there was no difficulty in effecting the pulling apart of these angles by 



