to any
irregularity occurring in the movement of the little planet or to its
eccentricity.

If one considers the vast size of the diameter KL, which according to
me is some 24 thousand diameters of the Earth, one will acknowledge
the extreme velocity of Light. For, supposing that KL is no more than
22 thousand of these diameters, it appears that being traversed in 22
minutes this makes the speed a thousand diameters in one minute, that
is 16-2/3 diameters in one second or in one beat of the pulse, which
makes more than 11 hundred times a hundred thousand toises; since the
diameter of the Earth contains 2,865 leagues, reckoned at 25 to the
degree, and each each league is 2,282 Toises, according to the exact
measurement which Mr. Picard made by order of the King in 1669. But
Sound, as I have said above, only travels 180 toises in the same time
of one second: hence the velocity of Light is more than six hundred
thousand times greater than that of Sound. This, however, is quite
another thing from being instantaneous, since there is all the
difference between a finite thing and an infinite. Now the successive
movement of Light being confirmed in this way, it follows, as I have
said, that it spreads by spherical waves, like the movement of Sound.

But if the one resembles the other in this respect, they differ in
many other things; to wit, in the first production of the movement
which causes them; in the matter in which the movement spreads; and in
the manner in which it is propagated. As to that which occurs in the
production of Sound, one knows that it is occasioned by the agitation
undergone by an entire body, or by a considerable part of one, which
shakes all the contiguous air. But the movement of the Light must
originate as from each point of the luminous object, else we should
not be able to perceive all the different parts of that object, as
will be more evident in that which follows. And I do not believe that
this movement can be better explained than by supposing that all those
of the luminous bodies which are liquid, such as flames, and
apparently the sun and the stars, are composed of particles which
float in a much more subtle medium which agitates them with great
rapidity, and makes them strike against the particles of the ether
which surrounds them, and which are much smaller than they. But I hold
also that in luminous solids such as charcoal or metal made red hot in
the fire, this same movement is caused by