360 FRAGMENTS OF SCIENCE. 
rises in a pump; the effect being then explained by the 
maxim that " Nature abhors a vacuum/' It was not known 
that there was any limit to the height to which the water 
would ascend, until, on one occasion, the gardeners of 
Florence, while attempting to raise water to a very great 
elevation, found that the column ceased at a height of 
thirty-two feet. Beyond this all the skill of the pump- 
maker could not get it to rise. The fact was brought to 
the notice of Galileo, and he, soured by a world which had 
not treated his science over kindly, is said to have twitted 
the philosophy of the time by remarking that nature 
evidently abhorred a vacuum only to a height of thirty- 
two feet. Galileo, however, did not solve the problem. 
It was taken up by his pupil Torricelli, to whom, after 
due pondering, the thought occurred, that the water might 
be forced into the tube by a pressure applied to the surface 
of the liquid outside. But where, under the actual circum- 
stances, was such a pressure to be found? After much 
reflection, it flashed upon Torricelli that the atmosphere 
might possibly exert this pressure; that the impalpable air 
might possess weight, and that a column of water thirty- 
two feet high might be of the exact weight necessary to 
hold the pressure of the atmosphere in equilibrium. 
There is much in this process of pondering and its results 
which it is impossible to analyze. It is by a kind of inspira- 
tion that we rise from the wise and sedulous contemplation 
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 the 
light of truth. This passage from facts to principles is 
called induction; and induction, in its highest form, is, as 
I have just stated, a kind of inspiration. But, to make it 
sure, the inward sight must be shown to be in accordance 
with outward fact. To prove or disprove the induction, 
we must resort to deduction and experiment. 
Torricelli reasoned thus: If a column of water thirty-two 
feet high holds the pressure of the atmosphere in equi- 
librium, 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- 
