There is, however, an important difference in the magazine, which has no spiral spring, but is furnished instead with an ingenious system of ratchet bars.

In most cases the motion is communicated by means of a detent,attached to some reciprocating part of the engine,to a ratchet wheel which gives motion to the other wheels in its slow revolution; but it is preferable to derive the motion from some revolving part of the engine by means of an endless screw, as where the ratchet is used the detent will sometimes fail to carry it round the proper distance.