Light is not a substance but is the effect produced on the eye by the impinging of the ripples of the ether upon the retina.

These waves are excessively minute, ranging in length from 1-39,000th of an inch at the red end of the spectrum to 1-57,000th at the violet end.

Next remember that these waves are not composed of advancing particles of the medium but pass onwards by the push which each particle in the line of motion gives to the particle next to it, and then you will see that if there were a break of one fifty-thousandth part of an inch in the connecting ether between our eye and any source of light we could not receive light from that source, for there would be nothing to continue the wave-motion across the gap.

Consequently as soon as we see light from any source however distant, we know that there must be a continuous body of ether between us and it.

Now astronomy shows us that we receive light from heavenly bodies so distant that, though it travels with the incredible speed of 186,000 miles per second, it takes more than two thousand years to reach us from some of them; and as such stars are in all quarters of the heavens we can only come to the conclusion that the primary substance or ether must be universally present.
This means that the raw material for the formation of solar systems is universally distributed throughout space; yet though we find that millions of suns stud the heavens, we also find vast interstellar spaces which show no sign of cosmic activity.