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results which it is impossible to analyze. It is by a kind of
inspiration that we rise from the wise and sedulous con-
templation of facts to the principles on which they depend.
The mind is, as it were, a photographic plate, which is
gradually cleansed by the effort to think rightly, and which
when so cleansed, and not before, receives impressions from
theolight of truth. This passage from facts to principles is
called induction, which in its highest form is inspiration;
but, to make it sure, the inward sight must be shown
to be in accordance with outward fact. To prove or dis-
prove the induction, we must resort to deduction and ex-

Torricelli reasoned thus: If a column of water thirty-
two feet high holds the pressure of the atmosphere in
equilibrium, a shorter column of a heavier liquid ought to
do the same.. Now, mercury is thirteen times heavier than
water; hence, if my induction be correct, the atmosphere
ought to be able to sustain only thirty inches of mercury.
Here, then, is a deduction which can be immediately sub-
mitted to experiment. Torricelli took a glass tube a yard
or so in length, closed at one end and open at the other,
and filling it with mercury, he stOpped the open end with
his thumb, and inverted it in a basin filled with the liquid
metal. One can imagine the feeling with which Torricelli
removed his thumb, and the delight he experienced when
he found that his thought had forestalled a fact never before
revealed to human eyes. The column sank, but ceased to
sink at a height of thirty inches, leaving the Torricellian
vacuum overhead. From that hour the theory of the pump
was established.

The celebrated Pascal followed Torricelli with a still
further deduction. He reasoned thus: If the mercurial
column be supported by the atmosphere, the higher we
ascend in the air the lower the column ought to sink, for
the less will‘be the weight of the air overhead. He ascend-

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