420 



Mr DENISON, ON SOME RECENT 



able for general use. And so I found that we were really as far as ever from a prac- 

 ticable gravity escapement, capable of satisfying all the requisite conditions. 



There were, as might be expected, several new gravity escapements in the Exhibition 



of 1851, but none of them by any means 

 perfect, or at all likely to come into use. 

 But there was also a new form of dead es- 

 capement, which had just before been patented 

 by Mr C. Macdowall, a clockmaker, and which 

 certainly possessed considerable advantages in 

 some respects over Graham's, or any escape- 

 ment of that class. It was called the single- 

 pin escapement, because the scape-wheel is 

 only a small disc with a single (ruby) pin in 

 it, parallel and very near to the arbor (or 

 axis) of the disc. The disc turns half round 

 at every beat of the pendulum, and the pin 

 gives the impulse on the vertical faces of the 

 pallets ; and the dead friction takes place on 

 the horizontal faces, as in the other dead 

 escapements. This drawing will sufficiently 

 explain its action. The principal advantage 

 of it is that the greatest part of the impulse 

 is nearly direct, and is therefore given with 

 hardly any friction ; and the consequence is, 

 that the pressure on the dead part of the 

 pallets is also much less than usual, so that 

 scarcely any oil is required. A further proof 

 of the small friction in this escapement is, 

 that I know a watch of this kind has been 

 going very well for above a year, and was 

 exposed on some cold nights last winter which 

 would have stopped a watch with a common 

 lever escapement. It is however an objec- 

 tion to it, that two additional wheels are 

 required in the train, and the last pivot has 

 to turn with such a velocity, that the force 

 on the scape-disc would be liable to vary a 

 good deal from variations in the state of the oil. 

 But it afterwards occurred to me that 

 this last objection might be removed, and 

 also the direct or middle portion of the im- 

 pulse retained, omitting altogether the oblique 



C. Macdowall's Single-pin Escapement. 





wm 



!a'Vh 



