65.--RESPONSES OF A WIRE TO AMPLITUDES OF VIBRATION
45 deg. AND 90 deg.
(_a_) Responses when the wire was in a sluggish condition at temperature
of 5 deg. C.
(_b_) Enhanced response at 30 deg. C.
(_c_) Diminution of response at 90 deg. C.]

#Diphasic variation.#--It has already been said that if two points A and B
are in the same physico-chemical condition, then a given stimulus will
give rise to similar excitatory electric effects at the two points. If
the galvanometer deflection is 'up' when A alone is excited, the
excitation of B will give rise to a downward deflection. When the two
points are simultaneously excited the electric variation at the two
points will _continuously_ balance each other. Under such conditions
there will be no resultant deflection. But if the intensity of
stimulation of one point is relatively stronger, then the balance will
be disturbed, and a resultant deflection produced whose sign and
magnitude can be found independently by the algebraical summation of the
individual effects of A and B.

It has also been shown that a balancing point for the block, which is
approximately near the middle of the wire, may be found so that the
vibrations of A and B through the same amplitude produce equal and
opposite deflection. Simultaneous vibration of both will give no
resultant current; when the block is abolished and the wire is vibrated
as a whole, there will still be no resultant, inasmuch as similar
excitations are produced at A and B.

After obtaining the balance, if we apply an exciting reagent like
Na_2CO_3 at one point, and a depressing reagent like KBr at the
other, the responses will now become unequal, the more excitable point
giving a stronger deflection. We can, however, make the two deflections
equal by increasing the amplitude of vibration of the less sensitive
point. The two deflections may thus be rendered equal and opposite, but
the time relations--the latent period, the time rate for attaining the
maximum excitation and recovery from that effect--will no longer be the
same in the two cases. There would therefore be no continuous balance,
and we obtain instead a very interesting diphasic record. I give below
an exact reproduction of the response-curves of A and B recorded on a
fast-moving drum. It will be remembered that one point was touched with
Na_2CO_3 and the other with KBr. By suitably increasing the
amplitude of vibration of the less sensitive, the two deflections we