s, so
called, did not appear to be really fixed, but that they described small
circles in the heavens each year. This fact greatly perplexed him, until
at last he hit upon the true solution by taking into account the motion
of the earth in its orbit, together with the fact that light had a
finite velocity. This result showed that the light from the stars
travelled with the same velocity as that which travelled from Jupiter's
satellites. The Aberration of Light, as his discovery was termed, may be
illustrated in the following way--Suppose that you are standing still,
and that it is raining, the rain descending vertically on the umbrella
that you hold up to cover you. As soon as you begin to walk, the
rain-drops will apparently begin to slant, and if the walk is changed
into a run, the greater apparently will be the slanting direction that
the rain-drops take. In the same way, the rays of light from a star
would fall vertically upon the earth if it were motionless, but as the
earth is moving through space with varying velocity, it gives to the
rays of light a slanting direction. By calculating the speed of the
earth, and ascertaining the exact slanting direction of the rays, the
velocity of light may be ascertained. This Bradley did, and showed that
it coincided almost with the result arrived at by Roemer. Various other
means have been adapted to test the results arrived at by these two
astronomers. Fizeau, in 1849, was able to measure the velocity of light
by using, not planetary or stellar distances, but by simply using
distances in the city of Paris; while Foucault, in 1860, devised a
method of measuring the velocity of light in air or any other medium.
The results arrived at by these men leave no doubt as to the exact speed
of light, which may now be reckoned to have a velocity of 186,000 miles,
or 300,000,000 metres per second. Notwithstanding this great speed at
which light travels, the nearest stars are so far off that their light
takes about 3-1/2 years to reach the earth, while scientists tell us
that some of the most distant stars are so remote, that their light
takes thousands of years to reach our earth, travelling at the rate of
186,000 miles per second. From considerations like these we get a dim
conception of the almost illimitable extent of the universe. Now let us
try to understand what this rate of motion really means. We have to
remember that light is caused by wave motions in the Aether, so that we
have