I, I, which is struck from the centre S'. Now
suppose that D moves to E, and if we take the radius D, H, and from E
mark it upon the arc I as at V, then H will obviously be the new
position of H. To find the new position of G we first strike the arc J,
J, because in every position of G it will be somewhere on the arc J, J.
To find where that will be when H is at V, take the radius H, G, and
from V as a centre mark it on J, J, as at K, which is the position of G
when D is at E and H is at V. For the positions when D is at F we repeat
the process, taking the radius D, H, and from F marking P, and with the
radius H, G, and from P as a centre marking Q; then P is the new
position for H, and Q is that for G.

[Illustration: Fig. 263.]

In Figure 264 a lever arm A and cam C are in one piece on a shaft. S is
a shoe sliding on the line _x_, and held against the cam face by the rod
R; it is required to find the position of the face of the shoe against
the cam when the end of the arm is at D.

Draw line E from D to the axis of the shaft and line F. From the shaft
axis as a centre draw circle W; draw line J parallel to _x_. Take the
radius G H, and from K as a centre mark point P on W; draw line Q from
the shaft axis through P, and mark point T. From the shaft axis as a
centre draw from T an arc, cutting J at V, and V is the point where the
face of the shoe and the face of the cam will touch when the arm stands
at D.

[Illustration: Fig. 264.]

Let it be required to find the amount of motion imparted in a straight
line to a rod attached to an eccentric strap, and the following
construction may be used. In Figure 265 let A represent the centre of
the shaft, and, therefore, the axis about which the eccentric revolves.
Let B represent the centre of the eccentric, and let it be required to
find in what position on the line of motion _x_, the centre C of the rod
eye will be when the centre B of the eccentric has moved to E. Now since
A is the axis, the centre B of the eccentric must rotate about it as
denoted by the circle D, and all that is necessary to find the position
of C for any position of eccentric is to mark the position of B on
circle D, as at E, and from that position, as from E, as a centre, and
with the length of the rod as a radius, mark the new position of C on
the line _x_ of its motion. With the centre of the eccentric at B, the
line Q, representing the faces of the straps, will stand at a right
angle to the line