IMPROVEMENTS IN CLOCK-ESCAPEMENTS. 427 



2. The approximate tripping is prevented by the length of the locking-teeth of the 

 scape-wheel ; for as their points are made three times as far from the center as the pins which 

 lift the arms, their pressure on the stops is so small that the friction due to it is not enough 

 to resist the weight of the arms ; and so, if they do by accident get thrown a little too high 

 by the scape-wheel, they immediately fall down again and rest against the pin which has lifted 

 them until the pendulum arrives. 



3. These long teeth (as in Mr Bloxam's escapement) also render the momentary friction 

 at unlocking quite insensible, and they will act perfectly well without any oil, though there 

 is no harm in putting a little oil on the stops, if it be only to keep them from rusting. 

 And there is no other friction in the escapement capable of affecting the pendulum ; for that 

 of the pivots on which the arms move, and the small amount of sliding of the fork-pins on the 

 beat screws in the pendulum-rod, are too small for any possible variation of such friction to be 

 of any consequence. These two frictions only correspond to those of the pallet-arbor and the 

 fork in a common dead escapement ; for there is always some sliding of the fork on the rod, 

 because no point of the pendulum moves in a circle, but in something like a cycloid, on account 

 of its suspension by a spring ; and moreover we saw that the pressure of the fork on the 

 pendulum in a common escapement must be at least five times as great as in an escapement 

 which has scarcely any friction. 



4. The difficulty of satisfying the proper mathematical condition in most other gravity 

 escapements is the risk of tripping, and the want of sufficient length of arms to make the 

 locking safe within the angle a — y, if y is made of the proper size. From what has been 

 said before, it is evident that no such difficulty exists here in satisfying the mathematical 



condition of <y = - ; and perhaps y= — is a more convenient size, and still more secure. 

 2 3 



5. The best proof of the facility with which this escapement can be made, and its con- 

 sequent cheapness, is the fact that two of them, one for a turret-clock and the other for a 

 regulator, were made immediately from my drawings, without any mistake, by Mr Dent's 

 ordinary workmen, in fact, chiefly by a boy ; and they say it is the easiest escapement to make 

 that there is. It is too soon yet to be able to give an exact estimate of the price for which these 

 clocks can be made ; but as we have now got an escapement independent of the friction of the 

 train, and there is nothing either of difficulty or delicacy in making it, I see no reason to 

 doubt that astronomical clocks may be made with this escapement for i?20, to go better than 

 those which have hitherto cost £80. It is true that a great deal of the work for which these 

 large sums are paid, is not worth a farthing to any body, contributing nothing to the accurate 

 performance of the clock, and being probably never seen by any body except the men who do 

 it, and who put the clock together, though the only pretence for doing it is that the clock- 

 makers think it looks well. But so long as a great part of the work must be highly finished, 

 and the clock-trade is carried on as it is in England, you will be obliged to pay for the 

 finishing in the same way of the rest of the work, though it would do just as well if it was 

 not • finished' at all : in fact it is by no means uncommon to see that greater attention has 

 been bestowed on the parts which required none, than on those which could not be done too 

 carefully. A gravity escapement which requires no great delicacy in construction will remove 



Vol. IX. Part III. 55 



