49
out of the top of the receiver and
sealed in place with cement. As
the pressure in the receiver was
reduced, the level of the mercury
fell. He also performed the opposite
experiment, and found that raising
the pressure inside the receiver
made the level of the mercury rise.
This confirmed the previous
findings of Torricelli and Pascal.
Boyle noted that it became
harder and harder to pump air out
of the receiver as the amount of air
left decreased, and also showed
that a half-inflated bladder in the
receiver increased in volume as
the air surrounding it was removed.
A similar effect on the bladder
could be achieved by holding it in
front of a fire. He gave two possible
explanations for the “spring” of
the air that caused these effects:
each particle of the air was
compressible like a spring and the
whole mass of air resembled fleece,
or the air consisted of particles
moving randomly.
This was similar to the view
of the Cartesians, although Boyle
did not agree with the idea of
the ether, but suggested that the
“corpuscles” were moving in
empty space. His explanation is
remarkably similar to the modern
kinetic theory, which describes
the properties of matter in terms
of moving particles.
Some of Boyle’s experiments
were physiological, investigating
the effects on birds and mice of
reducing the pressure of the
air, and speculating on how air
is moved in and out of lungs.Boyle’s law
Boyle’s law states that the pressure
of a gas multiplied by its volume
is a constant, as long as the amount
of gas and the temperature are
kept the same. In other words, if
you decrease the volume of a gas,
its pressure increases. It is this
increased pressure that produces
the spring of the air. You can feel
this effect using a bicycle pump
by covering the end with a finger
and pushing the handle in.
Although it bears his name,
this law was first proposed not by
Boyle, but by English scientists
Richard Towneley and HenrySCIENTIFIC REVOLUTION
If the height of the mercury
column is less on the top of a
mountain than at the foot of it,
it follows that the weight of the
air must be the sole cause of
the phenomenon.
Blaise Pascal
Power, who performed a series
of experiments with a Torricelli
barometer and published their
results in 1663. Boyle saw an early
draft of the book and discussed
the results with Towneley. He
confirmed them by experiment
and published “Mr Towneley’s
hypothesis” in 1662 as part of
a response to criticism of his
original experiments.
Boyle’s work on gases was
particularly significant because of
his careful experimental technique,
and also his full reporting of all his
experiments and their possible
sources of error, whether or not
they gave the expected results.
This led many to seek to extend his
work. Today, Boyle’s law has been
combined with laws figured out by
other scientists to form the “ideal-
gas law,” which approximates to
the behavior of real gases under
changes of temperature, pressure,
or volume. His ideas would also
eventually lead to the development
of the kinetic theory. ■This is because there is
less air above you
pressing down
on the mercury.This means that the
smaller the amount of
air in the receiver, the
lower its pressure.The height of mercury
in a barometer falls if
you take the barometer
up a mountain.The level of mercury falls
as air is pumped out of the
receiver in a barometer.The “spring of the air” decreases as
the mass of the air decreases.