John Wesley.

A survey of the wisdom of God in the creation; or, A compendium of natural philosophy .. (Volume 3) online

. (page 24 of 24)
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a lady's pocket book, she would guess it to be an enigma
for nothing \ and \\ouid be astonished to hear, that it is
the quintessence of a most metaphysical and most sub-
tle argument maintained by a most celebrated divine
and philosopher.

The only positive idea applied to space is extension*
But we can apply no idea to any subject, which the sub-
ject itself does not impress. Matter forces upon our
senses the idea of its extension. But how can we invest
with this, substance which never excited any idea in us
and consequently has no existence to us 1 Space is only
one; of the ideas excited by matter, and by the mind
abstracted from its subject, just as we can image a co-
lour to ourselves, without connecting any particular sub-
ject w kh it. A little more of the same metaphysics,
which can prove that nothing is extended, witt prove
that space is purple. But why should I say purple J



277

Space is of all* colours, if light is reflected by a vacuum
It is an ingenious contrivance, to render nothing a sub-
ject of conception, by dressing it in a suit of clothes
borrowed from something.

To illustrate the doctrine of space, a common experi-
ment shews, that by an image formed in the air, at &
certain distance between a concave glass, and any person
looking into it, extension becomes an object-of sense,
where there is neither solidity nor any sensible resist-*
ance. But this does not prove that an image is formed
in empty space, or where there is no matter : it rather
proves that these spaces which they call empty, are full
of matter. For as tbe senses can be affected only b>'
matter, they infallibly determine where matter is; So
that we are as sure there is matter where we see any
any thing, though we cannot feel it, as that it is there,
where we feel, though vve cannot see it.

10. Let us now more attentively consider the first
supposed law of motion, matter is indifferent to conti-
nue in motion or in rest,

Rest and metion are the the two greatest opposite? ia
nature, as opposite as matter and nothing. The mind
therefore cannot be struck with a more palpable contra-
diction, by affirming that a body is equally disposed to
hardness and softness at the same time, than by saying
it is equally disposed to rest and motion.

Motion is a positive thing, which implies- action,
power, or force, wherever it acts. Rest is a mere ne-
gative, a state wherein body is divested of all these. It
'exerts no power; it acts or presses, neither backward?
nor forwards, neither up nor down. Now the same
body cannot be indifferent to tbe exerting of power and
to the exerting of Rciie at the same time.

Again ; \t is impossible that rest and motion can be
equally indifferent to matter. When matter was created
should we suppose the Creator to say, ""Let it he,"
without determining in which of these states it should
commence bting 5. yet.it is impossible it could besin to
N 6*



27S

fee; bo tli moving and resting. It could assume only
one of these conditions, and must have remained therein
for ever, unless some farther -divine energy had given it
a new determination. Now in which ever of these
matter began to exist, that must be called its natural
state. Aud every alteration of that state must be the
effect of some power superinduced upen it, which must
ceiise when the cause ceases.

A^ain ; matter may exist in rest : but no living mat-
ter. All life in nature, whether mineral, vegetable, or
animal, depends upon motion and activity. Therefore
motion seems to be not the natural state of matter, but
superadded thereto, and constantly supported, in order
to constitute life, variety, and mutability. Tsow all
know, material motion proceeds upon, and is regulated
by mechanical iaws. And does not motion uniformly
conducted by the laws of mechanism, imply a constant
mechanical cause? This mechanical system is traceable
in most cases, even in the most subtle and elaborate
works of nature, such as plants and animals. And may
not the same heavens which influence every thing 01*
earth, rule the motions of the earth itself: and impress
all matter with these general tendencies, which are the
basis of all human mechanics 7

11. Proceed we to what is called the second law of
motion.

We can have no idea of power but that it is matter
in motion, or endeavouring to act. We cannot connect
the idea of power with matter at rest, unless that
rest be the effect of power fixing it i its place, which
we may term mechanical power. This rest, being an
effect of power, will exert a resistance to motion, when
it is pressed upon. But otherwise, matter can have na
such power in itself, can exert none ; because power
consists in motion, or a njsus to it* Therefore matter
resting unmechanically can have no nisus of any kind,
An iHirNecluinical nisus in matter to rest, is in other
words an active power exerted by it to do nothing.

The states then in motion or rest being the result of



279

absolute pa&siveuess in matter, and the effect of no po-
siiive nisus, an unmechanical matter can exert no resist-
ance to change the state : and of consequence an atom
would have as much power to move a planet, as a planet
to move an atom.

An action or tendency to action is plainly implied in
a nisus to any state. And as a nisus to passiveness is a,
contradiction in terms, it follows, that the properties of
power and motion, cannot be considered in matter taken
abstactediy, but qs composed into a system. Therefore,
though it must be allowed, that the changes of state in
matter are proportioned to the powers that produce
them, yet it is impossible to conceive, that the power
shall continue in the body acted upon, after the exterior
power ceases to act upon it.

12. The third supposed law of motion is this : when
matter is put into motion, it communicates as much re-
sistance towards stopping the motion of the body that
moves it, as it receives motion from it.

Philosophers never had it in their power to make the
experiments on which this law is grounded, upon any
bodies but such as were under the influence of gravita-
tion. And if this axiom can be proved to depend upon
gravitation, it must cease to be an axiom, as being only
an accident depending upon another acknowledged cause.

Resistance or re-action must be produced whereever
matter in motion encounters matter moving or tending
to move in an opposite or a different direction. Now
all bodies tend or gravitate toward the eariii. There-
fore this tendency must re-actor resist according to its
quantity, every power applied to move a gravitating
body in any other direction.

We have no way to estimate the quantify of matter
contained in any bo.dies, but. the quantity of their gra-
vitation. Hence we must necessarily infer, that the law
of re-action, is not according to the quantity of matter in
particular detached parcels thereof, but according to the



280

decree of their gravitation. For were the gravity of a
body but the half of what it is now, that body would re-
act but half as much as it does ; and of course, were all
its gravitation to cease, it would iiot re-act at all.

Again ; it is supposed, gravitation is twenty-three
times greater on the surface of the sun than on the sur-
face of the earth. Hence a body which weighs one
pound here, would there weigh three and twenty. Con-
sequently without any addition of matter, it would re-
act twenty three times more than it does here. There-
fore this re-actiori, supposed an absolute law of matter,
is only a circumstance depending on the relative law of
gravitation.

13. Come we now to the doctrine of centripetal and
centrifugal forces.

In another age it will be iuatter of universal wonder,
that one of the most profound mathematicians in the
world should assume two powers for circulating the pla-
nets, and even circulale the quantities of matter thereby
from the proportions wherein they must act in produ-
cing and maintaining the circuits of the moving stars :
while it is demonstrable to common sense, from the ad-
mitted nature of these two powers, that it is absolutely
impossible they can support one single rotation of an. orb;

Gravitation is allowed by all to be a constant power
in bodies, which cannot be altered but by change of
distance. It cannot be suspended ; for though its effect
may be resisted, yet its tendency thereto is invariable.
It is therefore a proper undestroyabie power, uninter-
ruptedly acting in and upon bodies.

The ItAvs assigned to projection are just the reverse.
When- any proportion of the quantity of projectile motion
is destroyed, either by direct Opposition, or by change
of its direction, it exerts no nisus to recover its first quan-
tity of motion. Consequently as long as any power,
such as that of gravitation, is bending the direction of
projection, it is a contiuual resistance of the power of



881

projection, which is continually diminished thereby.
And as it has no tendency to recover this, the smallest
continued resistance will at last quite exhaust its power,
though originally ever so great. Thus every projectile
on the earth, however great the projecting force may be
at setting out, is continually retarded till it rests in the
direction of a parabolic curve.

Sir Isaac seems not to have reflected on this circum-
stance of gravitation and projection, that the one retains*
its whole tendency to motion, whether it be retarded or
stopped, while the other always loses as much power as
it meets with opposition. Neither in balancing these
powers, does he seem to have reflected on that obvious
truth : that every alteration in the direction of a moving
projectile, destroys so much of its motion, which cannot
be repaired, but by a continued action of the first
moving cause.

Philosophers illustrate the joint effect of centripetal
and centrifugal force, in making bodies move in a circle,
by the experiment of casting round a weight, suspended
by a string in one's hand. But this illustration contains
a palpable deception. For the power of the string re-
straining the body from flying off in a strait line, bears
no analogy to a power actutually drawing a moving body
towards iis centre of motion. The string resists its
ftylug off, but has not the least tendency to draw it nearer.
And whatever is the cause of the revolution of the pla-
nets, it must be some cause which simply resists their
ying off into eccentric motions. It cannot in the nature
of things be one, which is uniformly drawing them into
their centre of motion.

But suppose both gravitation and projection had the
same property of still retaining their original tendency to
their respective motions, however they were retarded :
still it is impossible that these two powers, acting by
immutable laws, can move an orb any otherwise than in
a circle : whereas all the planets are allowed by philoso-
phers themselves to move in ellipsis.

These powers moving an orb hi the figure of an ellip-
sis, must H9 less than four times vary the proportion of



their several impulses, during every cornpleat revolution.
The power of gravitation is uniformly gaining on that of
projection, from the higher point of the ellipsis to the
lower. Now (not to ask how the projectile force reco-
vers itself, but supposing it had this property) I ask, by
what law does gravitation remit the strength it has gained,
in bringing the orb from the higher point to the lower,
and at that point allow projection to recover the force it
Lad lost, in order to carry it back to the higher point ?
In like manner seeing projection has been gaining on
gravitation, all the way to that point, how comes it all at
once to lose its superior force there ? And how comes
gravitation immediately to preponderate, in order to
bring the orb to the lower point again ]

It cannot be said, that the increased velocity, which
brings a planet to the lower, contributes to carry it back
to the higher point. For Unit increased velocity was not
the effect of projection, but of gravitation. Therefore
the orb can never get outward again, unless at that point,
gravitation all at once weakens its pull of the planet
inwards.

There is one circumstance more, which mathemati-
cians ought to consider well : namely,, that no figure
(circle or ellipsis) can be described by gravitation and
projection round lh<* centre of gravity, where the centre
of gravity shall not be found in the centre of the figure..
But this is contrary to all astronomical observation upon
the motion of the planets, which determines their centre
of gravity to be always in one of the foci of their ellipti-
cal orbits.

Yet farther. In order to move any body in a circle,
the moving powers must be equal, or nearly so. Now
the proportion ef the moving powers upon one body to
each other, can only be determined by the velocity of
the respective motions. Ii;deed, the quantity of motion
in different bodies must be determined by the quantity
of matter moving and velocities taken togelrier. But in
one and thesume body it may be determined solely by
the velocity of its motions.

Equal powers then- can only be determined by the-



283 .

equal quantities of motioii they produce. But as to tii
powers of gravitation and projection, the proportion be-
tween them, as ascertained by the ablest mathematicians,
is so far from being equal, that the immense disparity
between them, can scarce be reduced to a calculation.
Therefore it is utterly impossible that these two powers
should produce the revolution of the earth.

If the sun and earth were as near each other as the
earth and the moon are, and were left to the power of
their mutual attraction, they would move toward each
other with the same velocity as it is supposed the earth
and rnoon do, which I think is about sixteen feet in a
minute : except so far as the proportion of jpatter in the
earth to that in the sun, differs from that of the earth to
the moon. If then the earth at that distance from the
sun, would gravitate toward him with the velocity of
sixteen feet in a minute, and if the decrease of gravita-
tion, be inversely as the squares of the distances, (that
is, at double distances four times less) then the earth
being immensely farther from the sun than the moon
is from the earth, the velocity with which the earth at
her present distance from the sun would move towards
him, if left to the power of attraction, must be im-
mensely less than sixteen feet in a minute. But what is
the force which moves the earth sixteen feet or a thou-
sand, to the force of that projection, which is supposed
to move it at the rate of near a thousand miles in a
minute ?

In short, if the power of gravitation draws the earth
towards its centre of gravity, with the force of sixteen
feet, or sixteen hundred in a minute, while the powers
o* projection impresses it with the force of almost a
thousand miles in the same time, it is impossible for ma-
thematics to demonstrate that any orb hurried off by
such a projection, can ever be recalled from its eccentric
motion, by such an inconceivably small and dispropor-
tionate resistance : especially as the power of gravitation,
small as it is, must be growing smaller every moment,
Nor can the mathematical properties of an

4



284

or any figure, ever prove the gravitation, which is con-
tinually wasting and spinning out into a cobweb thread,
will at any point recover a superiority to the projectile
force, and grow at last a cable, massy and powerful
enough to bring home the wandering star again.

14. I would add some thoughts on the motion of the
satellites. It is no wonder that notwithstanding all the
arguments for the motion of the ear ih, yet the greatest
part of astronomers have not pronounced it absolutely
certain, but only probable in a high degree. Among the
perplexities which attend this highly probable system,
the doctrine of alsolute motion is not the smallest. It
is certain all the phenomena of relative motion, ure the
very same as if the earth were at rest. And it is not
easy to conceive how this can possibly be, on the suppo-
sition of the earth's motion.

The phenomena of bodies moving in the same direc-
tion with the absolute motion of the earth may be com-
prehended : that motion of bodies cross the absolute
motion of the earth is also intelligible. But it is no
easy matter to satisfy one's self about the phenomena
of bodies moving westward, or in an opposite direction
to that of absolute motion. If we should suppose that
a ball fired pointed blank west, does not really move
westward, but it is only resisted by the explosion from
moving so fast east as the earth goes in her absolute
course ; may it not be asked, What is it that keeps the
ball suspended, while the earth proceeds in her absolute
motion ] For the resistance given to the progressive
motion of the ball, can be no resistance to its following
the course of its gravity : as we have no example to ex-
plain how resistance applied horizontally will prevent a
body's falling to the ground in the same time as if it
was not so resisted. If the ball's absolute motion is
only the force of its vis inertice, derived from the earth's
motion, and its apparent motion in a contrary direction
is only from another vis inertice, derived from the ex-
plosion. What possible conception can be framed of
the ttvo opposite vis inertite's, acting so as to prevent a



2S5

body for some time from pursuing the course of its
gravity ?

On the other hand, if the motion westward is real t
it seems to imply a plain contradiction : for no body
can realiy move eastward and westward at one and the
same time.

But though the doctrine of projectiles could be recon-
ciled with the motion of the earth, yet what shall we say
of self-moving bodies ? That absolute motion which all
bodies are supposed to partake of, is not alledged to be
maintained iiithcin after they are separated from the earth,
by any other means than their vis inertia, or their retain-
ing the quantity of motion once impressed upon them.
Kon r no body can move in a direction opposite to its
vis inertice, till that is overcome. How is it conceivable
then, that birds, >r example, after they are separated
from the earth, where they acquired their absolute mo-
tion, should retain it all ] Certainly avery reluctation
of their's in an opposite direction, while on the wing,
must destroy part of their absolute motion, as they can-
not then have any fresh absolute motion communicated
to them. This should imply a great change in the phe-
nomena, with regard to the motion of self-moving bo-
dies : but in fact, all the phenomena are the same, as if
the earth were at rest. In short, the motion which bo-
dies have in common with the earth, is something which
no re-action has any effect on: therefore, it does not,
cannot depend upon the axioms of the present phi-
losophy.

When we come to apply the theory of absolute mo-
tion to the secondary planets, in whatever light we con-
sider it, it becomes a matter utterly inconceivable, nay,
impossible. In the first place, 'we "know of no absolute
motion, communicated from greater to smaller bodies,
but where they are so intimately connected, that gravi-
tation at last, yea soon, destroys all their projectile mo-
tion. But such is the distance of the moon from the
earth, and so remote is their connection, that her gravi-
tation has never gained any thing upon her projectile
motion.



286

Again ; the moon, suppose her present distance from
the eavth to be her original one, could never, by means
of the weak connection of gravitaiiou, correspond with
their projection of the earth. Suppose the moon at her
present distance, and behind the earth, just in the course
of the earth's projection; in this situation, suppose the
moon advances toward the earth, at the rate of sixteen
feet in a minute, while the earth projected away from
the moon near a thousand miles in the same time : can
any one suppose, that this imperceptible motion of the
moon toward the earth, would draw the moon with the
iorce of the earth's absolute motion? This supposition
is attended with the same manifest impossibilities, in
whatever part of her circle the moon is considered, at
the moment of projection. Suppose her in her first
quadrature : then the gravitation between them and the
projection of the earth lying nearly in the same direc-
tion, nothing could prevent their collision in a few hours :
and till they had met, their mutual gravitation could
have no effect in communicating the absolute motion of
the earth to the moon. Yet supposing that the projec-
tion of the moon round the earth, commenced at the-
same instant with the projection of the earth, does not
help ; for as it is not that projection which gives the moon
her absolute motion, the whole impossibility remains,
yea, and is renewed every month in every supposable
circumstance. For it is as impossible her absolute
motion can be maintained by such means, as that it
shouldco mmence by them.

It is no less impossible, that the moon's absolute
motion can be owing to a projection given to herself,
than that it should be owing to her gravitation toward
the earth : for this plain reason ; because she has a pro-
jectile motion quite different from this, namely round
the earth* For nothing is more impossible, than for a
body to move in two directions at the same t!*ie. If
five hundred projections, all in different directions, were
applied at the same time, the projectile would fall into
one course, common to them all.

Add to this, that if there can be no real motion, man,



287

adverse direction to absolute motion, unless there be a
destruction, or at least weakening of this vis inertice,
which is supposed to be the principle that continues ab-
solute motion: then the projectile course of the moon
round the earth, must soon destroy her absolute motion.
For every month the moon fdr near 500,000 miles, strug-
gles in a course, which is in effect, diametrically opposite
to the vis inertia, currying her iia another direction.
And this cannot happen without continually weakening,
and at last wholly destroying it.

For these reasons, unless I can see them fairly re-
moved, 1 must conclude, that even supposing these prin-
ciples, assumed by the present philosophy, are real, yet
it is impossible to explain the celestial motions by them.



END OF THE THIRD VOLUME.




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Online LibraryJohn WesleyA survey of the wisdom of God in the creation; or, A compendium of natural philosophy .. (Volume 3) → online text (page 24 of 24)