where Y equals the displacement of T to some scale dependent on the
constants of the instrument.
If the whole block of templets be now pushed under the points P and if the
drawing-board be moved at the same rate, then the pen T will draw the curve
Y = F([xi]). The instrument now is an _integraph_ giving the value of a
definite integral as function of a _variable parameter_.
Having thus shown how the lever with its springs can be made to serve a
variety of purposes, we return to the description of the actual instrument
constructed. The machine serves first of all to sum up a series of harmonic
motions or to draw the curve