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no little worry to the great Philosopher. Some of those who attacked him enjoyed considerable
and, it must be admitted, even well-merited repute in the ranks of science. They alleged,
however, that the elongation of the coloured band which Newton had noticed was due to this,
to that, or to the other--to anything, in fact, rather than to the true cause which Newton
assigned. With characteristic patience and love of truth, Newton steadily replied to each such
attack. He showed most completely how utterly his adversaries had misunderstood the
subject, and how slight indeed was their acquaintance with the natural phenomenon in
question. In reply to each point raised, he was ever able to cite fresh experiments and adduce
fresh illustrations, until at last his opponents retired worsted from the combat.
It has been often a matter for surprise that Newton, throughout his whole career, should have
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taken so much trouble to expose the errors of those who attacked his views. He used even to
do this when it plainly appeared that his adversaries did not understand the subject they were
discussing. A philosopher might have said, "I know I am right, and whether others think I am
right or not may be a matter of concern to them, but it is certainly not a matter about which I
need trouble. If after having been told the truth they elect to remain in error, so much the
worse for them; my time can be better employed than in seeking to put such people right."
This, however, was not Newton's method. He spent much valuable time in overthrowing
objections which were often of a very futile description. Indeed, he suffered a great deal of
annoyance from the persistency, and in some cases one might almost say from the rancour, of
the attacks which were made upon him. Unfortunately for himself, he did not possess that
capacity for sublime indifference to what men may say, which is often the happy, possession
of intellects greatly inferior to his.
The subject of optics still continuing to engross Newton's attention, he followed up his
researches into the structure of the sunbeam by many other valuable investigations in
connection with light. Every one has noticed the beautiful colours manifested in a soap-bubble.
Here was a subject which not unnaturally attracted the attention of one who had expounded
the colours of the spectrum with such success. He perceived that similar hues were produced
by other thin plates of transparent material besides soap-bubbles, and his ingenuity was
sufficient to devise a method by which the thicknesses of the different films could be
measured. We can hardly, indeed, say that a like success attended his interpretation of these
phenomena to that which had been so conspicuous in his explanation of the spectrum. It
implies no disparagement to the sublime genius of Newton to admit that the doctrines he put
forth as to the causes of the colours in the soap-bubbles can be no longer accepted. We must
remember that Newton was a pioneer in accounting for the physical properties of light. The
facts that he established are indeed unquestionable, but the explanations which he was led to
offer of some of them are seen to be untenable in the fuller light of our present knowledge.
Had Newton done nothing beyond making his wonderful discoveries in light, his fame would
have gone down to posterity as one of the greatest of Nature's interpreters. But it was
reserved for him to accomplish other discoveries, which have pushed even his analysis of the
sunbeam into the background; it is he who has expounded the system of the universe by the
discovery of the law of universal gravitation.
The age had indeed become ripe for the advent of the genius of Newton. Kepler had
discovered with marvellous penetration the laws which govern the movements of the planets
around the sun, and in various directions it had been more or less vaguely felt that the
explanation of Kepler's laws, as well as of many other phenomena, must be sought for in
connection with the attractive power of matter. But the mathematical analysis which alone
could deal with this subject was wanting; it had to be created by Newton.
At Woolsthorpe, in the year 1666, Newton's attention appears to have been concentrated
upon the subject of gravitation. Whatever may be the extent to which we accept the more or
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less mythical story as to how the fall of an apple first directed the attention of the philosopher
to the fact that gravitation must extend through space, it seems, at all events, certain that this
is an excellent illustration of the line of reasoning which he followed. He argued in this way.
The earth attracts the apple; it would do so, no matter how high might be the tree from which
that apple fell. It would then seem to follow that this power which resides in the earth by
which it can draw all external bodies towards it, extends far beyond the altitude of the loftiest
tree. Indeed, we seem to find no limit to it. At the greatest elevation that has ever been
attained, the attractive power of the earth is still exerted, and though we cannot by any actual
experiment reach an altitude more than a few miles above the earth, yet it is certain that
gravitation would extend to elevations far greater. It is plain, thought Newton, that an apple
let fall from a point a hundred miles above this earth's surface, would be drawn down by the
attraction, and would continually gather fresh velocity until it reached the ground. From a
hundred miles it was natural to think of what would happen at a thousand miles, or at
hundreds of thousands of miles. No doubt the intensity of the attraction becomes weaker with
every increase in the altitude, but that action would still exist to some extent, however lofty
might be the elevation which had been attained.
It then occurred to Newton, that though the moon is at a distance of two hundred and forty
thousand miles from the earth, yet the attractive power of the earth must extend to the moon.
He was particularly led to think of the moon in this connection, not only because the moon is
so much closer to the earth than are any other celestial bodies, but also because the moon is
an appendage to the earth, always revolving around it. The moon is certainly attracted to the
earth, and yet the moon does not fall down; how is this to be accounted for? The explanation
was to be found in the character of the moon's present motion. If the moon were left for a
moment at rest, there can be no doubt that the attraction of the earth would begin to draw
the lunar globe in towards our globe. In the course of a few days our satellite would come
down on the earth with a most fearful crash. This catastrophe is averted by the circumstance
that the moon has a movement of revolution around the earth. Newton was able to calculate
from the known laws of mechanics, which he had himself been mainly instrumental in
discovering, what the attractive power of the earth must be, so that the moon shall move
precisely as we find it to move. It then appeared that the very power which makes an apple
fall at the earth's surface is the power which guides the moon in its orbit.
Once this step had been taken, the whole scheme of the universe might almost be said to [ Pobierz całość w formacie PDF ]

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