In what manner is the transmission effected? We cannot imagine the ether behaving in a way void of all system.
The answer is, by a wave motion. The ether must be regarded as a very elastic solid. The agitation of a portion of it by what we call heat, light, or electricity, sets in motion adjoining particles, until they are moving from side to side, but not forwards; the resultant movement resembling that of a snake tethered by the tail.
These ether waves vary immensely in length. Their qualities and effects upon our bodies or sensitive instruments depend upon their length. By means of ingenious apparatus the lengths of various waves have been measured. When the waves number 500 billion per second, and are but the 40,000th of an inch long they affect our eyes and are named light—red light. At double the number and half the length, they give us the sensation of violet light.
When the number increases and the waves shorten further, our bodies are “blind” to them; we have no sense to detect their presence. Similarly, a slower vibration than that of red light is imperceptible until we reach the comparatively slow pace of 100 vibrations per second, when we become aware of heat.
Ether waves may be compared to the notes on a piano, of which we are acquainted with some octaves only. The gaps, the unknown octaves, are being discovered slowly but surely. Thus, for example, the famous X-rays have been assigned to the topmost octave; electric waves to the notes between light and heat. Forty years ago Professor Clerk Maxwell suggested that light and electricity were very closely connected, probably differing only in their wave-length. His theory has been justified by subsequent research. The velocity of light (185,000 miles per second) and that of electric currents have been proved identical. Hertz, a professor in the university of Bonn, also showed (1887-1889) that the phenomena of light—reflection, refraction, and concentration of rays—can be repeated with electric currents.
We therefore take the word of scientists that the origin of the phenomena called light and electricity is the same—vibration of ether. It at once occurs to the reader that their behaviour is so different that they might as well be considered of altogether different natures.
For instance, interpose the very thinnest sheet of metal between a candle and the eye, and the light is cut off. But the sheet will very readily convey electricity. On the contrary, glass, a substance that repels electricity, is transparent, i.e. gives passage to light. And again, electricity can be conveyed round as many corners as you please, whereas light will travel in straight lines only.
To clear away our doubts we have only to take the lighted candle and again hold up the metal screen. Light does not pass through, but heat does. Substitute for the metal a very thin tank filled with a solution of alum, and then light passes, but heat is cut off. So that heat and electricity both penetrate what is impenetrable to light; while light forces a passage securely barred against both electricity and heat. And we must remember that open space conveys all alike from the sun to the earth.
On meeting what we call solid matter, ether waves are influenced, not because ether is wanting in the solid matter, but because the presence of something else than ether affects the intervening ether itself. Consequently glass, to take an instance, so affects ether that a very rapid succession of waves (light) are able to continue their way through its interstices, whereas long electric waves are so hampered that they die out altogether. Metal on the other hand welcomes slow vibrations (i.e. long waves), but speedily kills the rapid shakes of light. In other words, transparency is not confined to light alone. All bodies are transparent to some variety of rays, and many bodies to several varieties. It may perhaps even be proved that there is no such thing as absolute resistance, and that our inability to detect penetration is due to lack of sufficiently delicate instruments.