A diminution of temperature contracts the air
in the bulb, causes the mercury to rise in the side of the tube, and
closes the valve.' Besides this, there was 'an improved
magneto-electric machine, for medical use, with a new arrangement, by
which the shock is graduated by means of a glass tube, in which a wire
is made to communicate with water, so as to produce at first a slight
shock; by gradually pressing down the wire attached to a spiral
spring, the shock is received in its full force.'
It now appears that Mr Robertson of Brighton claims priority of
discovery touching the boring power of _Pholades_. His statements are
founded on daily observation of the creatures at work for three
months. 'The _Pholas dactylus_' he says, 'makes its hole by grating
the chalk with its rasp-like valves, licking it up, when pulverised,
with its foot, forcing it up through its principal or bronchial
syphon, and squirting it out in oblong nodules. The crypt protects the
_Pholas_ from confervae, which, when they get at it, grow not merely
outside, but even within the lips of the valves, preventing the action
of the syphons. In the foot there is a gelatinous spring or style,
which, even when taken out, has great elasticity, and which seems the
mainspring of the motions of the _Pholas dactylus_.
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