330 
On Water and Air. 
[May, 
Well, these Florentine gardeners came to Galileo, and 
said : “ We want to get up water 50 or 60 feet from our 
pump, but we find that it will not rise to a greater height 
than 32 feet.” The explanation of the pump in those days 
was what ? No explanation at all. It is amazing how the 
words of a great man can bewilder the world ; and that not 
for a generation, or a century, but for thousands of years. 
And so it was with Aristotle. He gave an explanation, or, 
at least, his school gave an explanation of why water rises 
in a pump. The pump, as you know, is a cylinder with an 
attached valve, and into this cylinder is inserted a piston. 
Now, if I lift up this piston there is left behind it what is 
called a vacuum, that is, a space in which there is no air. 
And Aristotle’s statement was that, as nature abhorred a 
vacuum, this empty space could not be allowed to exist, and 
the water ran up to fill the vacuum. Well, Galileo was 
rather soured by the treatment he had received at the hands 
of the world. He looked at these gardeners, and he said : 
“ It is quite obvious that nature does not abhor a vacuum 
beyond a height of 30 or 32 feet.” However, the problem 
was not solved by Galileo. It fell into the hands of his 
celebrated pupil, Torricelli. Torricelli reasoned thus : — 
“ The atmosphere has weight. Here is a vessel, say, con- 
taining water. The atmosphere presses upon that water ; 
and if I, by means of my pump, remove the atmosphere, and 
so take away xhe pressure of the atmosphere above the 
water, the pressure of the atmosphere outside will cause the 
water to ascend.” And what does that show ? A thought 
occurred. First of all, remember, it was only a thought ; 
and that is the way that scientific men advance. They 
gather up together the knowledge prevalent in their times, 
and they ask themselves what is likely to result from this 
knowledge. Torricelli divined the reason with his mind’s 
eye before a human eye ever saw the fadrt. He said : “ If I 
remove the atmospheric pressure from the interior of my 
pump, the pressure outside will force the water up ; and 
that column of 32 feet that those gardeners in Florence 
lifted by their pump answers to the outside pressure of the 
atmosphere. The 32 feet of water holds the weight of the 
whole atmosphere in equilibrium.” This was his conjecture, 
but he did not content himself with that reason. He said : 
“ If my reason be correct — if it be the faCt that 32 feet of 
liquid water can hold the pressure or weight of the atmo- 
sphere in equilibrium — then, if I take a heavier liquid than 
water, I must have a shorter column supported. The weight 
of the atmosphere being a constant thing, will lift a shorter 
