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The following pages were originally prepared in the form
of a course of Lectures to be delivered before the Lowell
Institute, of Boston, Mass., but, owing to the unexpected
circumstance of the author's receiving no invitation to lecture
before that institution, they were laid aside shortly after
their completion.

Receiving an invitation from the trustees of the Vallecetos
Literary and Scientific Institute, during the present
summer, to deliver a course of Lectures on any popular subject,
the author withdrew his manuscript from the dusty
shelf on which it had long lain neglected, and, having some-what
revised and enlarged it, to suit the capacity of the
eminent scholars before whom it was to be displayed, repaired
to Vallecetos. But, on arriving at that place, he

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learned with deep regret, that the only inhabitant had left a
few days previous, having availed himself of the opportunity
presented by a passing emigrant's horse,—and that, in consequence,
the opening of the Institute was indefinitely postponed.
Under these circumstances, and yielding with reluctance
to the earnest solicitations of many eminent scientific
friends, he has been induced to place the Lectures before the
public in their present form. Should they meet with that
success which his sanguine friends prognosticate, the author
may be induced subsequently to publish them in the form of
a text-book, for the use of the higher schools and universities;
it being his greatest ambition to render himself useful
in his day and generation, by widely disseminating the information
he has acquired among those who, less fortunate,
are yet willing to receive instruction.