camera obscura, optics deal
exclusively with such inanimate materials; and hence the student
who studies them will do well to remember, that optics are the
science of vision, with the _fact_ of vision left entirely out of
the consideration.

* * * * *

ON THE BEST MEANS OF ESTABLISHING A COMMERCIAL INTERCOURSE
BETWEEN THE ATLANTIC AND PACIFIC OCEANS.

To shorten the navigation between the eastern and western divisions of our
globe, either by discovering a north-west passage into the Pacific, or
opening a route across the American continent, with European philosophers
and statesmen has for centuries been a favourite project, and yet in only
one way has it been attempted. Large sums of money were successively voted
and expended, in endeavouring to penetrate through the Arctic sea; and
such is the persevering enterprise of our mariners, that in all likelihood
this gigantic task eventually will be accomplished: but, even if it should,
it is questionable whether a navigable opening in that direction would
prove beneficial to commerce. The floating ice with which those high
latitudes are encumbered; the intricacy of the navigation; the cold and
tempestuous weather generally prevailing there, and the difficulty of
obtaining aid, in cases of shipwreck, must continue to deter the ordinary
navigator from following that track.

Enquiry, therefore, naturally turns to the several points on the middle
part of the American continent, where, with the aid of art, it is supposed
that a communication across may be effected. These are five in number, and
the facilities for the undertaking which each affords, have been discussed
by a few modern travellers, commencing with Humboldt. On a close
investigation into the subject, it will, however, appear evident, that
although the cutting of a canal on some point or order, may be within the
compass of human exertion, still the undertaking would require an enormous
outlay of capital, besides many years to accomplish it; and even if it
should be completed, the result could never answer the expectations formed
upon this subject in Europe. On all the points proposed, and more
especially in reference to the long lines, the difficulty of rendering
rivers navigable, which in the winter are swelled into impetuous torrents;
the want of population along the greater part of the distances to be cut;
the differences of elevation; and, above all, the s