332 
On Water and Air. 
[May, 
shall have a column of mercury that exactly balances the 
weight of the atmosphere. And there it is, as Torricelli 
foresaw with the eyes of his mind, the mercury falls until 
it reaches the point A, the column of mercury, A b (Fig. 36), 
being about 30 inches in length. 
If I take a tube of water instead of mercury, when I in- 
vert the tube you will find no depression of the column. 
The tube will remain full, because the weight of the atmo- 
sphere is quite sufficient to keep it full. I invert a tube of 
water over a vessel of water in the same manner as I did 
with the mercury, and I withdraw my hand, and the tube 
remains full, as I anticipated. Here we have, then, this 
celebrated Torricellian experiment, on which our present 
barometers depend. 
But another wise experiment followed this conjecture of 
Torricelli. There was a great man in those days named 
Pascal, and he, writing to his brother-in-law, M. Perrier, 
proposed an experiment to test the result of Torricelli. He 
had no doubt of the correctness of the result ; but still as 
a philosopher he thought himself in duty bound to test it 
in all possible ways, for in the days to which I refer there 
was a contest between the philosophic spirit, which has now 
got such complete predominance in the world, and the old 
Aristotelian spirit, which explained these things in such an 
extraordinary and unscientific fashion ; and hence it is that 
experiments like those proposed by Pascal had an extraordi- 
nary value, because it was the time of conflict between the 
era of scientific investigation and that era of loose specula- 
tion which had preceded it. Pascal wrote to his brother-in- 
law desiring him to make an experiment upon a celebrated 
mountain in Auvergne, “ for,” said Pascal, “ if it be that 
the rising of a column of mercury is due to the pressure of 
the atmosphere, when we go higher into the atmosphere 
that column of mercury ought to diminish. The column of 
mercury supported at the top of the hill ought to be less in 
height than the column supported at the sea-level.” Pascal’s 
remarks at the time were very quaint, and at the same time 
very sarcastic, because it must be remembered that they 
were uttered in the midst of a controversy between the new 
and the preceding philosophy. Pascal writes thus to his 
brother-in-law “ You see that if it happens that the 
weight of the mercury at the top of the hill is less than at 
the bottom (which I have many reasons to believe, though 
all those who have thought about it are of a different 
opinion),”— that is, the preceding philosophers,— ' it will 
follow that the weight and pressure of the air are the sole 
