August, 1904.] 



KNOWLEDGE & SCIENTIFIC NEWS. 



179 



The original ether was the " quintessence " of tlie 

 ancients — a kind of matter vaguely imagined as pure 

 and incorruptible enough to serve for the raw material 

 of the heavenly bodies, the four common elements being 

 reserved exclusively for sublunary use. The distinction, 

 however, eventually broke down. All the spheres, 

 from the frimum mobile to the \ery surface of our low- 

 earth, are pervaded by a subtle mode of action, de- 

 manding for its transmission machinery of a finer kind 

 than could be constructed out of gross everyday matter. 

 The phenomena of light, when they came to be atten- 

 tively studied, imperatively required a medium, uni- 

 versally diffused, evasive to sense, accessible only l^v 

 processes of reasoning. Hooke and Newton accord- 

 ingly brought the ether through the Horn-gate of 

 dream-land into a region of reality, where it became a 

 subject of legitimate speculation to men of science. 

 The task, however, of definitely specifying its qualities 

 was not taken serioush' in hand until the beginning of 

 the nineteenth century, when the establishment of the 

 undulatory theory of light supplied tangible holding- 

 ground for ideas regarding the vehicle of transmission, 

 and rendered the ether a fixture of thought. 



A great deal is demanded from it. We cannot afford 

 to set up an establishment of ethers; one factotum must 

 suffice. Incongruous otlices are devolved upon it. It 

 has to be Atlas and Mercury in one. It is the universal 

 supporter and the universal messenger. Whatever 

 kind of influence, or form of energy, can pass from 

 world to world, is conveyed by its means. If " action 

 at a distance " be inadmissible (as Newton himself held 

 it to be), the pull of gravity must be exerted through a 

 .medium; and common sense insists upon its identilica- 

 tion with the transmitting medium of light and electri- 

 city. That its dictate is actually complied with is 

 rendered virtually certain by Hertz's discovery that an 

 electric explosion starts an undulatory disturbance in- 

 distinguishable, except in scale, from luminous waves; 

 coupled with the indications derived from Mr. 

 Whittaker's recent mathematical researches to the 

 effect that a swifter beat of the same ethereal wings 

 bears the mandates of gravity. The unity of the medium 

 may then be regarded as finally ascertained; the com- 

 plex interactions of sundry different " fluids " need no 

 longer be taken into account. To provide one with the 

 capabilities implied by the services we perceive it to 

 render is, indeed, a sufliciently formidable task. 



In popular apprehension, the ether of space figures 

 as a finer kind of air. No idea could be more mislead- 

 ing. The elasticity by which air transmits the longi- 

 tudinal waves of sound is totally different from the 

 elasticity by which ether propagates the transversal 

 waves of light. Air yields to pressure; disturbance 

 hence produces in it undulatory condensations due to 

 oscillations of the gaseous molecules along the line in 

 which the audible commotion travels. Ether, on the 

 contrary, appears to be entirely incompressible; it con- 

 veys no vibrations directed lengthwise. Now this is 

 extremely perplexing. We have no experience of a 

 kind of matter absolutely rigid to pressure, while yield- 

 ing, albeit with intense reluctance, to distortional 

 stresses. A jelly-like solid makes the nearest, though 

 a very distant approach to fulfilling the indispensable- 

 conditions; and a solid ether was accordingly in vogue 

 until long past the middle of the nineteenth century. 

 For a solid, it had very peculiar qualities; th:it, for 

 instance, of offering no resistance to motion. It was, 

 in truth, obviously a mere temporary expedient — a 

 scientific fiction which might pass muster until replaced 

 by something Cf)rresponding less distantly with the 

 fundamental fact. M last, on the advent of the 



electro-magnetic theory of light and the modified con- 

 ceptions which it brought in its train, the solid ether 

 withdrew behind the scenes. Its properties, thoiii;h 

 inconsistent and unconvincing, h.-ul not been chosen 

 arbitrarily; they were imposed by the neccessities of the 

 situation; and when these varied, s[)tH:ulators naturally 

 had recourse to fresh inventions. 



The most plausible is that of a medium neither solid, 

 liquid, nor gaseous in the ordinary sense, but in the 

 ideal state of a " perfect fiuid." Out. of such an ether, 

 Lord Kehin, with exquisite ingenuity, constructed his 

 " vortex-atoms," which " had their day and ceased to 

 be." Other ideas now prevail. The present tendency 

 of physical science," the late Mr. I'reston wrote in 

 l.Syo,-'- " is to regard all the phenomena of Nature, and 

 even matter itself, as manifestations of energy stored 

 in the ether." The more closely we look into the things 

 around us, the more strongly the persuasion is forced 

 upon us that what we call ether, electricity, and 

 matter are really varied forms of one primal substance. 

 Two comprehensive schemes of molecular physics, rest- 

 ing upon the basis of this unifying thought, have lately 

 been elaborated, one by Dr. I.armor, the other by Pro- 

 fessor Osborne Reynolds. They have nothing in 

 conmion except the largeness of their synthesis. In 

 every respect they arc radically unlike, save in regard- 

 ing the intangible ether as the one material actuality. 

 Dr. Larmor, however, is not quite confidently explana- 

 tory. He presents no cut-and-dried theory of the uni- 

 verse; its haunting mysteries are not ignored in his 

 efforts to rationalise them. Thus, he is vividly aware 

 of the diOicullies besetting the endowment of the ether 

 with the type of elasticity which it is rcognised to 

 possess. He can only surmise that it results from 

 particular modes of motion — from " kinetic stability 

 ensuing upon a special dynamical state. The medium 

 may thus be thought of as pervaded by "a structure of 

 tangled or interlaced vortex filaments, which might re- 

 sist deformation by forming a stable configuration."! 

 But the details of any such scheme of action are 

 evidently far too intricate to be unravelled offhand; 

 what concerns us here is to point out that no simple, 

 structureless fluid can avail to maintain cosmical com- 

 munications. 



Dr. Larmor's conception of the ether, reduced to its 

 lowest terms, is that of a " rotationally elastic 

 medium."; In other words, it resists being turned 

 round an axis. The forces, however, continually act- 

 ing upon it are of a gyratory nature; and hence arise 

 strains, betrayed to our apprehension by electrical 

 phenomena. Each " electron " is held to be the nucleus 

 of some kind of distortion or displacement, § and 

 carries with it, as it moves, a field of force. Out of 

 these "point charges," material atoms are variously 

 built up. They are " structures in the ether," encom- 

 passed by " atmospheres of ethereal strain," not — as 

 they were formerly taken to be — " small bodies exert- 

 ing direct action at a distance on other atoms accord- 

 ing to extraneous laws of force. "11 Obviously, the 

 new- view brings to the front extremely subtle questions 

 regarding the nature of " dynamical transmission "!| — 

 w-hat the propagation of energy essentially consists in, 

 and by what mechanism it is effected ; and they are, 



♦ Theory of Light, 2nd Ed., p. 28. 



t Encyclopedia liril.. Vol. XXV., p. 106. 



t Report Brit. Asa., 1900, p. 626. 



{ Aether and Matter, p. 26. 



'i Nature, Vol. LXII , p 453- 



■I Larmor. Report lint Ass , ujoo, p. 625. 



