SL WEE-GAM TRAINS.
461
extended treatment under Applied Kinematics. It was only necessary to point out that the click-wheel with its sharp teeth belongs strictly to the class of slider-cam trains, 55 which on their
FIG. 328.
part also become, under certain circumstances, spur-wheel trains. We must now turn to some compound mechanisms which are
formed from click-gear.*
121. Ratchet-trains^
The common forms of ratchet-gear play apparently a somewhat subordinate part in machinery, for which perhaps their force-closed motions may account. None the less do they require our most careful attention, for reasons which I shall show further on, and we must therefore here make ourselves familiar with their principal characteristics.
- The slider-earn train which we might indicate by the contracted formula (CC )Z P)
has, like the chain (C'^C Z ;}, been frequently used as chamber-gear, not unfrequently with a force-closed sliding-block. It will be sufficient to mention, merely as illustra- tions of the form taken by the chain when chambered, the engines of Davies (Burn, Steam-Engine, p. 128), Scheutz (D. K. Clark, Exhibited Machinery of 1862, p. 318), or Sudlow {Engineering, Ap. 10, 1874, p. 267). The higher pairing in these machines again renders any attempt to form them into satisfactory steam-engines quite useless.
t See note p. 455.
