ent should grow slower in
proportion as it is shared over a greater quantity of matter, in
moving away from the source of the light, it could not conserve this
great velocity over great distances. But by supposing springiness in
the ethereal matter, its particles will have the property of equally
rapid restitution whether they are pushed strongly or feebly; and thus
the propagation of Light will always go on with an equal velocity.

[Illustration]

And it must be known that although the particles of the ether are not
ranged thus in straight lines, as in our row of spheres, but
confusedly, so that one of them touches several others, this does not
hinder them from transmitting their movement and from spreading it
always forward. As to this it is to be remarked that there is a law of
motion serving for this propagation, and verifiable by experiment. It
is that when a sphere, such as A here, touches several other similar
spheres CCC, if it is struck by another sphere B in such a way as to
exert an impulse against all the spheres CCC which touch it, it
transmits to them the whole of its movement, and remains after that
motionless like the sphere B. And without supposing that the ethereal
particles are of spherical form (for I see indeed no need to suppose
them so) one may well understand that this property of communicating
an impulse does not fail to contribute to the aforesaid propagation
of movement.

Equality of size seems to be more necessary, because otherwise there
ought to be some reflexion of movement backwards when it passes from a
smaller particle to a larger one, according to the Laws of Percussion
which I published some years ago.

However, one will see hereafter that we have to suppose such an
equality not so much as a necessity for the propagation of light as
for rendering that propagation easier and more powerful; for it is not
beyond the limits of probability that the particles of the ether have
been made equal for a purpose so important as that of light, at least
in that vast space which is beyond the region of atmosphere and which
seems to serve only to transmit the light of the Sun and the Stars.

I have then shown in what manner one may conceive Light to spread
successively, by spherical waves, and how it is possible that this
spreading is accomplished with as great a velocity as that which
experiments and celestial observations demand. Whence it may be
further remarked that although the particles a