ish all that the so-called chemical waves
accomplish, and that being so, the third Rule of our Philosophy is also
fulfilled, as we have in the aetherial electric waves a satisfactory
explanation for the fact which we seek to explain, viz. the character
and origin of the chemical waves that exist in the violet end of the
spectrum. Thus, we learn, that not only is the sun the source of all
heat and light, in that it gives rise to the vibrations of the Aether
which are propagated through it in waves, but that it is also the source
of all electric waves in the solar system, in that electric currents are
primarily due to the wave motion set up in the Aether, those electric
waves also traversing space with the velocity of light.

[Footnote 14: _Phil. Mag._, 1867.]

ART. 74. _Direction of Ray of Light._--In Art. 65 it was shown that the
direction of a ray of heat was that of a straight line from the heated
or luminous body from which the Aether waves proceeded. We have also
seen in Art. 69 that the aetherial waves which give rise to the
phenomena of heat are identical with those that give rise to light, so
the direction of a ray of light must also be that of a straight line
proceeding from the luminous body. A ray of light is a line
perpendicular to the Aether waves which are propagated through space in
concentric spheres from the luminous body, which, by its atomic
vibrations, gives rise to the light waves. It must, however, be
remembered that rays have no physical existence, for it is the waves
that are propagated, and not the ray, which simply indicates the
direction that the light takes, this truth being known as the
rectilineal propagation of light. That light proceeds in straight lines
may be proved in several ways. For example, we cannot see round corners,
which would be possible if light took a curved path instead of a
straight one. A better proof, however, may be obtained by making a small
hole in the window-shutter, and allowing the sunlight to pass into the
darkened room. The beam of light which passes into the room will then be
seen to take a straight course, its presence being revealed by the
particles of dust that float about the room.

Another conclusive proof that light proceeds in straight lines is to be
found in the fact, that all images formed on any screen by the rays of
light after passing through a small hole are inverted. For example,
suppose we have a window-shutter with a small hole in it, while in