the same as with
water. Ordinarily I use tap-water as the electrolyte. Zinc wires in
ZnSO_4 solution give responses similar in character to those given by,
for example, Pt or Sn in water.

#Test experiment.#--It may be urged that the E.M. effect is due in some
way (1) to the friction of the vibrating wire against the liquid; or (2)
to some unknown surface action, at the point in the wire of the contact
of liquid and air surfaces. This second objection has already been
completely met in experimental modification, fig. 55, _b_, where the
wire was shown to give response when kept completely immersed in water,
variation of surface being thus entirely eliminated.

Both these questions may, however, be subjected to a definite and final
test. When the wire to be acted on is clamped below, and vibration is
imparted to it, a strong molecular disturbance is produced. If now it be
carefully released from the clamp, and the wire rotated backwards and
forwards, there could be little molecular disturbance, but the liquid
friction and surface variation, if any, would remain. The effect of any
slight disturbance outstanding owing to shaking of the wire would be
relatively very small.

We can thus determine the effect of liquid friction and surface action
by repeating an experiment with and without clamping. In a tin wire
cell, with interposed external resistance equal to one million ohms, the
wire A was subjected to a series of vibrations through 180 deg., and a
deflection of 210 divisions was obtained. A corresponding negative
deflection resulted on vibrating the wire B. Now A was released from the
clamp, so that it could be rotated backwards and forwards in the water
by means of the handle. On vibrating the wire A no measurable deflection
was produced, thus showing that neither water friction nor surface
variation had anything to do with the electric action. The vibration of
the still clamped B gave rise to the normal strong deflection.

As all the rest of the circuit was kept absolutely the same in the two
different sets of experiments, these results conclusively prove that
the responsive electro-motive variation is solely due to the molecular
disturbance produced by mechanical vibration in the acted wire.

A new and theoretically interesting molecular voltaic cell may thus be
made, in which the two elements consist of the _same metal_. Molecular
disturbance is in this case the main source of energy. A cell once made
may be kep