Letters on England [30]
both that which carries the planets round the sun, as well
as the other which supposes every planet to turn on its own axis.
First, with regard to the pretended little vortex of the earth, it
is demonstrated that it must lose its motion by insensible degrees;
it is demonstrated, that if the earth swims in a fluid, its density
must be equal to that of the earth; and in case its density be the
same, all the bodies we endeavour to move must meet with an
insuperable resistance.
With regard to the great vortices, they are still more chimerical,
and it is impossible to make them agree with Kepler's law, the truth
of which has been demonstrated. Sir Isaac shows, that the
revolution of the fluid in which Jupiter is supposed to be carried,
is not the same with regard to the revolution of the fluid of the
earth, as the revolution of Jupiter with respect to that of the
earth. He proves, that as the planets make their revolutions in
ellipses, and consequently being at a much greater distance one from
the other in their Aphelia, and a little nearer in their Perihelia;
the earth's velocity, for instance, ought to be greater when it is
nearer Venus and Mars, because the fluid that carries it along,
being then more pressed, ought to have a greater motion; and yet it
is even then that the earth's motion is slower.
He proves that there is no such thing as a celestial matter which
goes from west to east since the comets traverse those spaces,
sometimes from east to west, and at other times from north to south.
In fine, the better to resolve, if possible, every difficulty, he
proves, and even by experiments, that it is impossible there should
be a plenum; and brings back the vacuum, which Aristotle and
Descartes had banished from the world.
Having by these and several other arguments destroyed the Cartesian
vortices, he despaired of ever being able to discover whether there
is a secret principle in nature which, at the same time, is the
cause of the motion of all celestial bodies, and that of gravity on
the earth. But being retired in 1666, upon account of the Plague,
to a solitude near Cambridge; as he was walking one day in his
garden, and saw some fruits fall from a tree, he fell into a
profound meditation on that gravity, the cause of which had so long
been sought, but in vain, by all the philosophers, whilst the vulgar
think there is nothing mysterious in it. He said to himself; that
from what height soever in our hemisphere, those bodies might
descend, their fall would certainly be in the progression discovered
by Galileo; and the spaces they run through would be as the square
of the times. Why may not this power which causes heavy bodies to
descend, and is the same without any sensible diminution at the
remotest distance from the centre of the earth, or on the summits of
the highest mountains, why, said Sir Isaac, may not this power
extend as high as the moon? And in case its influence reaches so
far, is it not very probable that this power retains it in its
orbit, and determines its motion? But in case the moon obeys this
principle (whatever it be) may we not conclude very naturally that
the rest of the planets are equally subject to it? In case this
power exists (which besides is proved) it must increase in an
inverse ratio of the squares of the distances. All, therefore, that
remains is, to examine how far a heavy body, which should fall upon
the earth from a moderate height, would go; and how far in the same
time, a body which should fall from the orbit of the moon, would
descend. To find this, nothing is wanted but the measure of the
earth, and the distance of the moon from it.
Thus Sir Isaac Newton reasoned. But at that time the English had
but a very imperfect measure of our globe, and depended on the
uncertain supposition of mariners, who computed a degree to contain
but sixty English miles, whereas it consists in
as the other which supposes every planet to turn on its own axis.
First, with regard to the pretended little vortex of the earth, it
is demonstrated that it must lose its motion by insensible degrees;
it is demonstrated, that if the earth swims in a fluid, its density
must be equal to that of the earth; and in case its density be the
same, all the bodies we endeavour to move must meet with an
insuperable resistance.
With regard to the great vortices, they are still more chimerical,
and it is impossible to make them agree with Kepler's law, the truth
of which has been demonstrated. Sir Isaac shows, that the
revolution of the fluid in which Jupiter is supposed to be carried,
is not the same with regard to the revolution of the fluid of the
earth, as the revolution of Jupiter with respect to that of the
earth. He proves, that as the planets make their revolutions in
ellipses, and consequently being at a much greater distance one from
the other in their Aphelia, and a little nearer in their Perihelia;
the earth's velocity, for instance, ought to be greater when it is
nearer Venus and Mars, because the fluid that carries it along,
being then more pressed, ought to have a greater motion; and yet it
is even then that the earth's motion is slower.
He proves that there is no such thing as a celestial matter which
goes from west to east since the comets traverse those spaces,
sometimes from east to west, and at other times from north to south.
In fine, the better to resolve, if possible, every difficulty, he
proves, and even by experiments, that it is impossible there should
be a plenum; and brings back the vacuum, which Aristotle and
Descartes had banished from the world.
Having by these and several other arguments destroyed the Cartesian
vortices, he despaired of ever being able to discover whether there
is a secret principle in nature which, at the same time, is the
cause of the motion of all celestial bodies, and that of gravity on
the earth. But being retired in 1666, upon account of the Plague,
to a solitude near Cambridge; as he was walking one day in his
garden, and saw some fruits fall from a tree, he fell into a
profound meditation on that gravity, the cause of which had so long
been sought, but in vain, by all the philosophers, whilst the vulgar
think there is nothing mysterious in it. He said to himself; that
from what height soever in our hemisphere, those bodies might
descend, their fall would certainly be in the progression discovered
by Galileo; and the spaces they run through would be as the square
of the times. Why may not this power which causes heavy bodies to
descend, and is the same without any sensible diminution at the
remotest distance from the centre of the earth, or on the summits of
the highest mountains, why, said Sir Isaac, may not this power
extend as high as the moon? And in case its influence reaches so
far, is it not very probable that this power retains it in its
orbit, and determines its motion? But in case the moon obeys this
principle (whatever it be) may we not conclude very naturally that
the rest of the planets are equally subject to it? In case this
power exists (which besides is proved) it must increase in an
inverse ratio of the squares of the distances. All, therefore, that
remains is, to examine how far a heavy body, which should fall upon
the earth from a moderate height, would go; and how far in the same
time, a body which should fall from the orbit of the moon, would
descend. To find this, nothing is wanted but the measure of the
earth, and the distance of the moon from it.
Thus Sir Isaac Newton reasoned. But at that time the English had
but a very imperfect measure of our globe, and depended on the
uncertain supposition of mariners, who computed a degree to contain
but sixty English miles, whereas it consists in