Year: 1874

HOW He Proved its Correctness.


What Sir Isaac Newton did was no


to discover gravitation, for every ont


who ever saw a stone fall saw an effec


of that force. He only discovered thai


gravitation extended into the celestial


spaces. His first reasoning was this


we see that all bodies at the surface oi


the earth tend to fall toward its centre.


This tendency is seen on the highest


mountains as well as at the surface OF


the ocean. How far does it extend up


ward? Why should it not extend to
| the moon? We know that the moon is


revolving around the earth, and without
| some force to keep it in its orbit around


the earth it would fly off irto space,


and we should soon lose sight of it.
Why should not this force, by which


the moon is continually turned aside
from the line IN which il is moving and


kept in path around the earth, be the


same force which causes a stone to fall


to the ground? To answer these ques-


tions, Newton began by calculating


what force would really be required to


keep the moon in her curved orbit


around the earth, and comparing it with


the force which caused heavy bodies 10


fall to the earth's surface, with the view


to learning whether the two forces we're
inversely as the square of the distance
from the earth's centre. Now allow me
to state circumstance which illustrates
the exactness of true scientific reason
g in reaching these conclusions. In
lis first calculations Newton found that
the two forces did not correspond. Had
he been any other than a man of true
T hn ko1
something so as to make them CORE
spond. Instead of doing so, he laid his
theory aside for a number of years. At
length he learned that more accurate
measurements of the size of the earth
than those accessible to him when he
made his calculations had been executed
by the French astronomers, and that
these gave for the size of the earth in
English miles a quantity much larger
than that which he had used in making
his calculations. He now found that
when he based his computations on the
true magnitude of the earth, the two
forces of the stone toward the earth
and the moon in its orbit corresponded
exactly to the theory. We see from
this that Newton did not discover gravi-
tation itself, but only that it extended
into the celestial spaces.


Not only does the moon move around
the earth, but all the planets move
around the sun. If no force acted on
them, they would move forward in a
straight line forever, and soon be lost in
the celestial spaces. The very fact that |
they move in curved orbits around the |
sun shows that they must be acted upon |
by some force directed toward the sun. |
The most care III and exact observations |
bha were made showed that this force |
was at all times and in the case of all the |
planets directed accurately toward the |
centre of the sun. Knowing the relative
distance of the various planets from the
sun, it was easy to calculate how strong
his force must be in the case of each,
md the result showed that in the case
If each different planet it's intensity was
nversely as the planets distance from
he sun. It remained only to show
whether the elliptic orbit in which each
planet was known to move around the
un would be produced by force in
'ersely as the square of the distance.
This required mathematical investiga-
ion which the scientific men of that day
ound very difficult; but Newton at
ength succeeded in solving the problem
n a manner which left no doubt. 1t
vas now proved that each and every
Janet was held in it's curved orbit by
orce acting directly toward the sun,
nd being inversely as the square
f the distance of the planet from it.
IS this force was to all appearance of
the same nature with that
1hich made the moon tend toward the
arth, it was quite reasonable to call it
ravitation. It differs from the force
-hich makes stone fall only in being
irected toward the sun instead of the ]
arth. -Harper's Magazine. ,