every test applied to the
phenomenon of light, adds additional strength to the undulatory theory,
at the expense of the Newtonian theory of emission. As light occupies
time in traversing space, it must follow from the theory that it does
not come from the radiant point exactly in straight lines, inasmuch as
the ether itself is in motion tangentially,--the velocity being in the
sub-duplicate ratio of the distances from the sun inversely.

May not that singular phenomenon,--the projection of a star on the
moon's disc, at the time of an occultation,--be due to this curvature of
the path of a ray of light, by considering that the rays from the moon
have less intensity, but more mechanical momentum, and consequently
more power to keep a straight direction? Let us explain: we have urged
that light, as well as heat, is a mechanical effect of atomic motion,
propagated through an elastic medium; that, _ceteris paribus_, the
product of matter by its motion is ever a constant quantity for equal
spaces throughout the universe,--in a word, that it is, and must
necessarily be, a fundamental law of nature. All departures from this
law are consequences of accidental arrangements, which can only be
considered of temporary duration. Our knowledge of planetary matter
requires the admission of differences in the density, form, and size of
ultimate atoms, and, according to the above law, when the atoms are of
uniform temperature or motion, the product of the matter of each by its
motion, when reduced to the same space, will be constant. The momentum
of two different atoms, therefore, we will consider equal, for the sake
of illustration; yet this momentum is made up of two different
elements,--matter and motion. Let us exaggerate the difference, and
assign a ratio of 1000 to 1. Suppose a ball of iron of 1000 lbs.,
resting upon a horizontal plane, should be struck by another ball of 1
lb., having a motion of 1000 feet in a second, and, in a second case,
should be struck by a ball of 1000 lbs., having a velocity of 1 foot per
second, the momentum of each ball is similar; but experience proves that
the motion impressed on the ball at rest is not similar; the ponderous
weight and slow motion is far more effective in displacing this ball,
for the reason that time is essential to the distribution of the motion.
If the body to be struck be small as, for instance, a nail, a greater
motion and less matter is more effective than much matter and little