shell of the tortoise, and sticks in it." Analogous calculations--if
such physico-mental operations can property be so called--are made in
the use of other missiles; for no projectile flies in a right line to
its mark. But the exact training of the eye lies at the bottom of them
all, and marksmanship depends almost wholly upon the power of that
organ, whose directions the blind muscles implicitly follow. Savages
accustomed only to the use of the bow become good shots with firearms
after very little practice. It is perhaps not out of place to observe
here that our English word aim comes from the Latin aestimo, I calculate
or estimate. See Wedgwood's Dictionary of English Etymology, and the
note to the American edition, under Aim.

Another proof of the control of the limbs by the eye has been observed
in deaf-and-dumb schools, and others where pupils are first taught to
write on large slates or blackboards. The writing is in large
characters, the small letters being an inch or more high. They are
formed with chalk or a slate pencil firmly grasped in the fingers, and
by appropriate motions of the wrist, elbow, and shoulder, not of the
finger joints. Nevertheless, when a pen is put into the hand of a pupil
thus taught, his handwriting, though produced by a totally different set
of muscles and muscular movements, is identical in character with that
which he has practised on the blackboard. For a very remarkable account
of the restoration of vision impaired from age, by judicious training,
see Lessons in Life, by Timothy Titcomb, lesson xi. It has been much
doubted whether the artists of the classic ages possessed a more perfect
light than those of modern times, or whether, in executing their minute
mosaics and gem engravings, they need magnifiers. Glasses ground convex
have been found at Pompeii, but they are too rudely fashioned and too
imperfectly polished to have been of any practical use for optical
purposes. But though the ancient artists may have had a microscopic