DIRECT AND REVERSED CLICK-TRAINS. 459
may be called the reversal of a click train. It is well suited for such a purpose as bringing into action at a given moment mecha- nical energy which has been stored up in any part of a machine. Click-trains used for this purpose may be called curb-gear; they are employed in many forms, of which an extremely familiar one is the common gun-lock. In this the two "bents" of the tumbler are the teeth of the click-piece or curb, which are released by
FIG. 324. FIG. 325.
pulling the trigger. Long ago, in the cross-bow of the middle ages and the catapults and ballistas of the ancients, the principle of the curb-gear was used in mechanisms by which stored-up energy was brought suddenly into action ( 48). In important modern machinery it serves the same purpose ; in the self-acting spinning machine, for example, both free and fast click-trains are used as curb-gear, the special object here being the effecting of a required change of motion at a given instant*
12 - Reversed Motion in Free Click-trains.
The applications of both forms of click-gear are as our examples have shown extremely numerous and important, more important, indeed, than they appear to be at first sight. This makes it necessary to examine somewhat more closely the mechanisms formed from them, several of which will throw considerable light
- Click-trains have not unfrequently been turned into chamber-gear, generally in
the form (C^Ct ;)l ,( V) = b,c. This is the formula, for^instance, for Watt's well- known rotary engine, in which the revolving piston is simply a one-toothed click wheel. This was patented by "Watt in 1782, and afterwards by Routledge in 1818, (see Farey, Steam- Engine, p. 672, PI. XV.), but naturally enough it was unsuccess- ful, the higher pairing C t ; Z could never be steam-tight, and was alone sufficient to destroy its efficiency
