rame is abolished, and the horizontal motion of P (Fig. 3), the guide
point, is produced by putting the whole frame on friction rollers; in
the second place, as a necessary result of the first change, the guide
point carries about with it its own polar system, which renders the
changes in length of "rays" much more manageable. f f, f' f' is a
frame moving on four roughed wheels, e e e e, so that it can only move
in the direction, f', which we may term horizontal. f f and f' f' are
rails guiding the chariots, A and B, from f to f and from f' to f'. Of
these chariots, A contains the guide point, P, to trace out the
primitive with, and B the pencil, P', to draw the sum curve, i.e., the
tracer. The chariot, B, like Boys' tracer, is heavily loaded. g g is a
horizontal bar rigidly attached to the crossbars, q q and q' q', of
the frame. On g g is a movable pivot, to which h, which determines the
pole, k0 h being the polar distance. k0 is the position of a
second point, k, on the chariot, A, when the guide point, P, is on the
initial line, g g. l l is a bar with a long slot in it, in which work
the pivots, h and k; this bar represents the "ray." A projecting arm k
k' has been introduced to enable me to shorten the polar distance down
to 2 in. and under by removing the pivot, k to k'. m m is a bar
attached to the block, n, which runs on l l, so that m m is always
perpendicular to l l. On the chariot, B, is another bar, m' m',
capable of turning round the pivot, d, and always maintained parallel
to m m by the rods, m m', m m'. Attached to m' m' is a wheel, w,
whose axis is parallel to m' m'. This wheel, therefore, always moves
perpendicular to m' m', and therefore to m m; hence it moves parallel
to the ray, h k. A pencil, P', attached traces out the sum curve. If
we wish to use the machine as an integrator, we have merely to measure
the vertical distance traversed by P', or the distance B has run along
f' f'. This is done by means of a scale on f f'. If k be brought down
to k0, w runs parallel to g g, or P' traces out a horizontal
straight line, which is thus the base line. If k be fixed as near as
possible to k0, which is done by means of a screw in f f at k0,
the chariot, B, can be run down f' f' as nearly opposite to k0 as
can be guessed at; a horizontal line may then be drawn as base line,
and the guide point, P, brought into this line by a clamping screw
with which it is provided. The instrument is then ready for action.
Ther