Letters on England [33]
bids him beware of
confounding this name with what the ancients called occult
qualities, but to be satisfied with knowing that there is in all
bodies a central force, which acts to the utmost limits of the
universe, according to the invariable laws of mechanics.
It is surprising, after the solemn protestations Sir Isaac made,
that such eminent men as Mr. Sorin and Mr. de Fontenelle should have
imputed to this great philosopher the verbal and chimerical way of
reasoning of the Aristotelians; Mr. Sorin in the Memoirs of the
Academy of 1709, and Mr. de Fontenelle in the very eulogium of Sir
Isaac Newton.
Most of the French (the learned and others) have repeated this
reproach. These are for ever crying out, "Why did he not employ the
word iMPULSION, which is so well understood, rather than that of
ATTRACTION, which is unintelligible?"
Sir Isaac might have answered these critics thus: --"First, you have
as imperfect an idea of the word impulsion as of that of attraction;
and in case you cannot conceive how one body tends towards the
centre of another body, neither can you conceive by what power one
body can impel another.
"Secondly, I could not admit of impulsion; for to do this I must
have known that a celestial matter was the agent. But so far from
knowing that there is any such matter, I have proved it to be merely
imaginary.
"Thirdly, I use the word attraction for no other reason but to
express an effect which I discovered in Nature--a certain and
indisputable effect of an unknown principle--a quality inherent in
matter, the cause of which persons of greater abilities than I can
pretend to may, if they can, find out."
"What have you, then, taught us?" will these people say further;
"and to what purpose are so many calculations to tell us what you
yourself do not comprehend?"
"I have taught you," may Sir Isaac rejoin, "that all bodies
gravitate towards one another in proportion to their quantity of
matter; that these central forces alone keep the planets and comets
in their orbits, and cause them to move in the proportion before set
down. I demonstrate to you that it is impossible there should be
any other cause which keeps the planets in their orbits than that
general phenomenon of gravity. For heavy bodies fall on the earth
according to the proportion demonstrated of central forces; and the
planets finishing their course according to these same proportions,
in case there were another power that acted upon all those bodies,
it would either increase their velocity or change their direction.
Now, not one of those bodies ever has a single degree of motion or
velocity, or has any direction but what is demonstrated to be the
effect of the central forces. Consequently it is impossible there
should be any other principle."
Give me leave once more to introduce Sir Isaac speaking. Shall he
not be allowed to say? "My case and that of the ancients is very
different. These saw, for instance, water ascend in pumps, and
said, 'The water rises because it abhors a vacuum.' But with regard
to myself; I am in the case of a man who should have first observed
that water ascends in pumps, but should leave others to explain the
cause of this effect. The anatomist, who first declared that the
motion of the arm is owing to the contraction of the muscles, taught
mankind an indisputable truth. But are they less obliged to him
because he did not know the reason why the muscles contract? The
cause of the elasticity of the air is unknown, but he who first
discovered this spring performed a very signal service to natural
philosophy. The spring that I discovered was more hidden and more
universal, and for that very reason mankind ought to thank me the
more. I have discovered a new property of matter--one of the
secrets of the Creator--and have calculated and discovered the
effects of it. After this, shall people quarrel with
confounding this name with what the ancients called occult
qualities, but to be satisfied with knowing that there is in all
bodies a central force, which acts to the utmost limits of the
universe, according to the invariable laws of mechanics.
It is surprising, after the solemn protestations Sir Isaac made,
that such eminent men as Mr. Sorin and Mr. de Fontenelle should have
imputed to this great philosopher the verbal and chimerical way of
reasoning of the Aristotelians; Mr. Sorin in the Memoirs of the
Academy of 1709, and Mr. de Fontenelle in the very eulogium of Sir
Isaac Newton.
Most of the French (the learned and others) have repeated this
reproach. These are for ever crying out, "Why did he not employ the
word iMPULSION, which is so well understood, rather than that of
ATTRACTION, which is unintelligible?"
Sir Isaac might have answered these critics thus: --"First, you have
as imperfect an idea of the word impulsion as of that of attraction;
and in case you cannot conceive how one body tends towards the
centre of another body, neither can you conceive by what power one
body can impel another.
"Secondly, I could not admit of impulsion; for to do this I must
have known that a celestial matter was the agent. But so far from
knowing that there is any such matter, I have proved it to be merely
imaginary.
"Thirdly, I use the word attraction for no other reason but to
express an effect which I discovered in Nature--a certain and
indisputable effect of an unknown principle--a quality inherent in
matter, the cause of which persons of greater abilities than I can
pretend to may, if they can, find out."
"What have you, then, taught us?" will these people say further;
"and to what purpose are so many calculations to tell us what you
yourself do not comprehend?"
"I have taught you," may Sir Isaac rejoin, "that all bodies
gravitate towards one another in proportion to their quantity of
matter; that these central forces alone keep the planets and comets
in their orbits, and cause them to move in the proportion before set
down. I demonstrate to you that it is impossible there should be
any other cause which keeps the planets in their orbits than that
general phenomenon of gravity. For heavy bodies fall on the earth
according to the proportion demonstrated of central forces; and the
planets finishing their course according to these same proportions,
in case there were another power that acted upon all those bodies,
it would either increase their velocity or change their direction.
Now, not one of those bodies ever has a single degree of motion or
velocity, or has any direction but what is demonstrated to be the
effect of the central forces. Consequently it is impossible there
should be any other principle."
Give me leave once more to introduce Sir Isaac speaking. Shall he
not be allowed to say? "My case and that of the ancients is very
different. These saw, for instance, water ascend in pumps, and
said, 'The water rises because it abhors a vacuum.' But with regard
to myself; I am in the case of a man who should have first observed
that water ascends in pumps, but should leave others to explain the
cause of this effect. The anatomist, who first declared that the
motion of the arm is owing to the contraction of the muscles, taught
mankind an indisputable truth. But are they less obliged to him
because he did not know the reason why the muscles contract? The
cause of the elasticity of the air is unknown, but he who first
discovered this spring performed a very signal service to natural
philosophy. The spring that I discovered was more hidden and more
universal, and for that very reason mankind ought to thank me the
more. I have discovered a new property of matter--one of the
secrets of the Creator--and have calculated and discovered the
effects of it. After this, shall people quarrel with