composed of other parts and that their springiness consists in the
very rapid movement of a subtle matter which penetrates them from
every side and constrains their structure to assume such a disposition
as to give to this fluid matter the most overt and easy passage
possible. This accords with the explanation which Mr. Des Cartes gives
for the spring, though I do not, like him, suppose the pores to be in
the form of round hollow canals. And it must not be thought that in
this there is anything absurd or impossible, it being on the contrary
quite credible that it is this infinite series of different sizes of
corpuscles, having different degrees of velocity, of which Nature
makes use to produce so many marvellous effects.
But though we shall ignore the true cause of springiness we still see
that there are many bodies which possess this property; and thus there
is nothing strange in supposing that it exists also in little
invisible bodies like the particles of the Ether. Also if one wishes
to seek for any other way in which the movement of Light is
successively communicated, one will find none which agrees better,
with uniform progression, as seems to be necessary, than the property
of springiness; because if this movement 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
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