The velocity of light is thus ten thousand times greater
than the speed of the earth. But even though the wind blew ten
thousand times faster than the speed with which the boat was sailing
there would still be some change, though no doubt a very small
change, in the position of the vane when the boat was in progress
from the position it would have if the boat were at rest. It
therefore occurred to this most acute of astronomers that when the
telescope was pointed towards a star so as to place it apparently in
the centre of the field of view, yet it was not generally the true
position of the star. It was not, in fact, the position in which the
star would have been observed had the earth been at rest. Provided
with this suggestion, he explained the apparent movements of the
stars by the principle known as the "aberration of light." Every
circumstance was accounted for as a consequence of the relative
movements of the earth and of the light from the star. This
beautiful discovery not only established in the most forcible manner
the nature of the movement of light; not only did it illustrate the
truth of the Copernican theory which asserted that the earth revolved
around the sun, but it was also of the utmost importance in the
improvement of practical astronomy.
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