Mr. DENISON ON TURRET-CLOCK REMONTOIRS. 641 



fly makes twelve revolutions for one of the driving wheel, the fly-pins will only exert ^^th of the 

 pressure on the axis that the spikes on the driving wheel exert. The fly is very light and made of 

 thin brass, and is of itself a spring; and so its axis will not be stopped with a sudden shock, and 

 the impact of the end of the fly on the escape-wheel axis may be made inconsiderable. This axis 

 must be prolonged beyond the frame, to allow a fly of larger radius than the driving wheel to be 

 used, and must end in a cylinder about half an inch thick. If the remontoir is to be let off" every 

 thirty seconds, which is a better interval for observation than twenty, the projecting cylinder may 

 have two notches cut in it as before described, if the escape-wheel revolves in a minute. But 

 it is generally made to revolve in two minutes, in order to save a wheel in the train ; and in that 

 case the letting off may be done better than with a four-armed fly, by making two notches across the 

 end of the cylinder, at right angles to each other, one broad, and the other narrow and deeper, so 

 that a broad pin will pass through one of the notches only, and a narrow and long pin through the 

 other only. These pins are of course to be parallel to the axis of the fly ; and the fly pinion must 

 have half the number of leaves that the escape-wheel pinion has, whatever may be the number of 

 teeth of the driving wheel. A Church-clock is now making on this plan. I have added a 

 drawing of the material parts, placed in the way most convenient for shewing their action. 



E. B. DENISON. 



