lastic envelope.
Now we will look at the subject from the atomic standpoint, and see if
it is in accordance with Huyghens' principle of wave propagation.

We will suppose that an undulatory movement is started by a luminous
body at point _A_ situated in the Aether, and surrounded by that medium.
_A_ may represent a part of any luminous body, as the sun or star, while
_B_ _C_ and _B'_ _C'_ represent a segment of the aetherial envelopes
already referred to, which exist around the sun. We will further suppose
that the small dots surrounding the luminous body represent the
aetherial atoms forming the envelope, which transmit the impulse or
energy received from the atomic vibrations of the luminous body. As each
aetherial atom is moved or pushed forwards, each atom directly in
contact with it accepts and transmits the impulse. But each of these
atoms stands in relation to those in front of them, as they did in
relation to the first row of atoms, so to speak, and therefore exert a
corresponding impulse on the front row.

But the third row stands in relation to the fourth row as the second row
did to the third, and so on to infinity. Thus each atom being surrounded
by other atoms may be looked on as the centre of a new wave system, so
that every particle of the wave system is itself a centre of a new wave
system which is transmitted in all directions. As these innumerable and
minute wave systems co-operate with one another, they form a principal
wave system which is coincident with the surface of the spherical
envelope, part of which is represented by _B_ _C_. Then if we conceive of
all the aetherial atoms in part of the principal wave system _B_ _C_, as
themselves becoming the centre of wave propagation, by their wave
systems the principal wave will be transmitted further on into space to
another aetherial envelope _B'_ _C'_, which represents part of another
principal wave, which again is coincident with the surface of one of the
spherical aetherial envelopes. So that by the action of the aetherial
atoms which exist on all sides of the luminous body, the aetherial wave
can be transmitted from atom to atom in more or less spherical form.

Now let us compare this explanation of the transmission of light by an
atomic Aether with the celebrated Huyghens' principle which is thus
enunciated. "When an undulatory movement propagates itself through an
elastic medium, every _particle_ imitates the movement of the particle
first excit