n after the expiration of
60 seconds, whereas when a few vibrations had been given recovery was
entirely completed in 47 seconds (_b_). There was here little change in
the height of response.

[Illustration: FIG. 63
(_a_) Slow recovery of a wire in a sluggish condition.
(_b_) Quickened recovery in the same wire after a few vibrations.]

#Or (2) by heightened response.#--The removal of sluggishness by
vibration, resulting in increased molecular mobility, is in other
instances attended by increase in the height of response, as will be
seen from the two sets of records which follow (fig. 64). Cold, due to
prevailing frosty weather, had made the wires in the cell somewhat
lethargic. The records in (_a_) were the first taken on the day of the
experiment. The amplitudes of vibration were 45 deg., 90 deg., and 135 deg.. In
(_b_) are given the records of the next series, which are in every case
greater than those of (_a_). This shows that previous vibration, by
conferring increased mobility, had heightened the response. In this
case, removal of molecular sluggishness is attended by greater intensity
of response, without much change in the period of recovery. In
connection with this it must be remembered that greater strain
consequent on heightened response has a general tendency to a
prolongation of the period of recovery.

[Illustration: FIG. 64
(_a_) Three sets of responses for 45 deg., 90 deg., and 135 deg. vibration in a
sluggish wire.
(_b_) The next three sets of responses in the same wire; increased
mobility conferred by previous vibration has heightened the
response.]

It is thus seen that when the wire is in a sluggish condition,
successive vibrations confer increased molecular mobility, which finds
expression in quickened recovery or heightened response.

#Effect of temperature.#--Similar considerations lead us to expect that a
moderate rise of temperature will be conducive to increase of response.
This is exhibited in the next series of records. The wire at the low
temperature of 5 deg. C. happened to be in a sluggish condition, and the
responses to vibrations of 45 deg. to 90 deg. in amplitude were feeble. Tepid
water at 30 deg. C. was now substituted for the cold water in the cell, and
the responses underwent a remarkable enhancement. But the excessive
molecular disturbance caused by the high temperature of 90 deg. C. produced
a great diminution of response (fig. 65).

[Illustration: FIG.