hing the edge of the plate at different points when it
is bowed, different notes, and hence varying forms, are obtained (fig.
3). If the figures here given are compared with those obtained from the
human voice, many likenesses will be observed. For these latter, the
'voice-forms' so admirably studied and pictured by Mrs Watts Hughes,[1]
bearing witness to the same fact, should be consulted, and her work on
the subject should be in the hands of every student. But few perhaps
have realised that the shapes pictured are due to the interplay of the
vibrations that create them, and that a machine exists by means of which
two or more simultaneous motions can be imparted to a pendulum, and that
by attaching a fine drawing-pen to a lever connected with the pendulum
its action may be exactly traced. Substitute for the swing of the
pendulum the vibrations set up in the mental or astral body, and we have
clearly before us the _modus operandi_ of the building of forms by
vibrations.[2]

[Illustration: FIG. 3. FORMS PRODUCED IN SOUND]

[Footnote 1: _The Eidophone Voice Figures._ Margaret Watts Hughes.]

[Footnote 2: Mr Joseph Gould, Stratford House, Nottingham, supplies the
twin-elliptic pendulum by which these wonderful figures may be
produced.]

The following description is taken from a most interesting essay
entitled _Vibration Figures_, by F. Bligh Bond, F.R.I.B.A., who has
drawn a number of remarkable figures by the use of pendulums. The
pendulum is suspended on knife edges of hardened steel, and is free to
swing only at right angles to the knife-edge suspension. Four such
pendulums may be coupled in pairs, swinging at right angles to each
other, by threads connecting the shafts of each pair of pendulums with
the ends of a light but rigid lath, from the centre of which run other
threads; these threads carry the united movements of each pair of
pendulums to a light square of wood, suspended by a spring, and bearing
a pen. The pen is thus controlled by the combined movement of the four
pendulums, and this movement is registered on a drawing board by the
pen. There is no limit, theoretically, to the number of pendulums that
can be combined in this manner. The movements are rectilinear, but two
rectilinear vibrations of equal amplitude acting at right angles to each
other generate a circle if they alternate precisely, an ellipse if the
alternations are less regular or the amplitudes unequal. A cyclic
vibration may also be obtain