Why does a walking stick help a man on a journey?
Because he pushes against the ground with the stick, which may be
considered as compressing a spring between the earth and the end of his
stick, which spring is therefore pushing up as much as he pushes down; and
if, at the time, he were balanced in the scales of a weighing beam, he
would find that he weighed just as much less as he were pressing with his
stick.
Why is sea-sickness produced on shipboard?
Because man, strictly to maintain his perpendicularity, that is, to keep
the centre of gravity always over the support of his body, requires
standards of comparison, which he obtains chiefly by the perpendicularity
or known position of things about him, as on land; but on shipboard, where
the lines of the masts, windows, furniture, &c. are constantly changing,
his standards of comparison are soon lost or disturbed. Hence, also, the
reason why persons unaccustomed to the motion of a ship, often find relief
by keeping their eyes directed to the fixed shore, where it is visible, or
by lying on their backs, and shutting their eyes; and, on the other hand,
the ill-effects of looking over the side of the vessel at the restless
waves of the sea.
Why is the pendulum a time-keeper?
Because the times of the vibrations are very nearly equal, whether it be
moving much or little; that is to say, whether the arc described by it be
large or small.
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