there is no reason assignable, why the vibration m should arise,
rather than any other ad libitum.

It is fashionable to smile at Hartley's vibrations and vibratiuncles;
and his work has been re-edited by Priestley, with the omission of the
material hypothesis. But Hartley was too great a man, too coherent a
thinker, for this to have been done, either consistently or to any
wise purpose. For all other parts of his system, as far as they are
peculiar to that system, once removed from their mechanical basis, not
only lose their main support, but the very motive which led to their
adoption. Thus the principle of contemporaneity, which Aristotle had
made the common condition of all the laws of association, Hartley was
constrained to represent as being itself the sole law. For to what law
can the action of material atoms be subject, but that of proximity in
place? And to what law can their motions be subjected but that of
time? Again, from this results inevitably, that the will, the reason,
the judgment, and the understanding, instead of being the determining
causes of association, must needs be represented as its creatures, and
among its mechanical effects. Conceive, for instance, a broad stream,
winding through a mountainous country with an indefinite number of
currents, varying and running into each other according as the gusts
chance to blow from the opening of the mountains. The temporary union
of several currents in one, so as to form the main current of the
moment, would present an accurate image of Hartley's theory of the
will.

Had this been really the case, the consequence would have been, that
our whole life would be divided between the despotism of outward
impressions, and that of senseless and passive memory. Take his law in
its highest abstraction and most philosophical form, namely, that