The New Student's Reference Work/Ether
Ether, a medium of exceedingly great tenuity supposed to fill all known space, including that which we speak of as filled with ordinary matter. The necessity of such a medium was first recognized by Huygens, and was admitted by all other clear thinkers as soon as Römer discovered the fact that light travels with finite speed. For, when it has been shown that light requires eight minutes to travel from the sun to the earth, the query naturally arises as to what becomes of the light (i. e. luminous energy) between the time it leaves the sun and the time it reaches the earth. The simplest possible explanation is that it exists somewhere in the space between the sun and the earth. But in all our experience we have never found energy except as associated with matter. For the sake of simplicity, therefore, we may assume that in this case, also, that is, in free space—space devoid of ordinary matter—luminous energy is also associated with matter. We call this matter ether. Since, however, in the 2,000 years between the time of Hipparchus and the present we are unable to detect any certain change in the length of the year, and since no retarding effect seems to be exerted upon any of the other planets, we must assume that the ether is a medium of enormously less density than the most tenuous gas of which we know anything whatever. Kelvin estimates the density of ether as 9.36×10−19. Huygens, Young and Fresnel have proved, not only that light is a wave-motion, but that it consists of a transverse wave-motion. But transverse waves are possible only in a medium which possesses rigidity, i. e., in a solid medium. We are driven therefore to assume further that the ether is a solid; or, at least, that it behaves as a solid for motions as rapid as those which constitute light. Shoemakers’ wax is very brittle, as may be shown by striking it a quick blow with a hammer; but, if a hammer be laid upon a pan of shoemakers’ wax and allowed to remain, it will be observed that at the end of some days the hammer has sunk to the bottom of the wax, showing that the wax behaves as a fluid with regard to slow-acting forces. The ether may behave as a fluid with respect to the comparatively slow motion of the planets through it.
In 1864 Maxwell predicted and in 1888 Hertz proved experimentally, that electrical disturbances are propagated through space with the same speed as that of light. In other words, they proved that one and the same medium would answer for the propagation of light waves and electric waves.
Melloni and others had already proved that the laws of propagation of heat are identical with those of light. The cumulative evidence for thinking space filled with a ponderable medium of exceedingly minute density grows stronger every day. For the original suggestion of the modern ether, see Huygens’ Treatise on Light, translated in Harper’s Scientific Memoirs.