o
get on either block or pecker. For similar reasons there should be some
clearance between A and the pecker, _i.e._, the latter should only bear
at one point and not bed flat against A.

Another form of inertia governor is shown in fig. 26 of the hit and miss
type, which is employed by Messrs Capel & Co. on many of their engines.

It consists of three main parts--the brass arm L carried on a stud D, on
which it is free to move; the weight W, which carries the pecker P
pivoted at the upper end of L; and the pecker block B, which engages the
pecker when the engine requires a charge of gas.

The governing action is dependent upon the shape of the operating cam
from X to Y. (In the case already dealt with, the lever L serves to
operate both air and gas valves, and so one cam only is necessary; but
in this instance the gas valve is operated by a separate cam, and a
greater nicety of adjustment is obtainable.)

[Illustration: FIG. 26.]

If the speed of the engine is sufficiently high, the arm L is thrust
forward at such a rate that the weight W tends to lag behind, with the
result that P is raised above the notch in B, as shown by the dotted
lines in drawing. On the other hand, when the speed is too low, the arm
L will not be thrust forward with so great a degree of suddenness, the
weight W will have time to move with L, and the relative position of W
and P to L will remain the same. Hence, in the first case, when a
_further_ forward movement is given to L by the cam, the pecker P is
clear of B, and omits to open the gas valve V; in the second case, P
engages with B, and the gas valve is held open during the time the
portion of cam Y to Z is passing over the roller R on arm L.

The great drawback to some forms of governors is not that they fail to
govern well when new, but that no provision is made to ensure them
working steadily when a bit worn. The shape of the cam has everything to
do with the regular working of this form of governor.

Supposing our cam was of the shape shown in fig. 27, _i.e._, the
governing and opening portion all in one curve, it would cause the
pecker to move both _forward_ and in an _upward_ direction at the _same
time_, so that at the moment of engaging B, P might still be moving in
an upward direction, which would cause uncertainty of action, especially
if the tips of the engaging members were at all blunt through wear; and,
in all probability, P would fly off B after partially opening the g