January 14, 1909^ 



NA 7 URE 



physical proximity, and in denying action at a distance 

 across empty space I am not denying telepathy or other 

 activities of a non-physical kind ; for although brain dis- 

 turbance is certainly physical and is an essential con- 

 comitant of mental action, whether of the sending or 

 receiving variety, yet we know from the case of heat 

 that a material movement can be excited in one place at 

 ihe expense of corresponding movement in another, with- 

 out any similar kind of transmission or material connec- 

 tion between the two places; the thing that travels across 

 vacuum is not heat. 



In all cases where physical motion is involved, however, 

 I would have a medium sought for ; it may not be matter, 

 but it must be something; there must be a connecting 

 link of some kind, or the transference cannot occur. 

 There can be no attraction across really empty space ; 

 and even when a material link exists, so that the connec- 

 tion is obvious, the explanation is not complete, for when 

 the mechanism of attraction is understood it will be found 

 that a body really only moves because it is pushed by 

 something from behind. The essential force in nature is 

 the vis a tetg,o. So when we have found the "traces," 

 or discovered the connecting thread, we still run up 

 against the word " cohesion," and ought to be exercised 

 in our minds as to its ultimate meaning. Why the whole 

 of a rod should follow, when one end is pulled, is a matter 

 retjuiring explanation ; and the onlv e.xplanation that can 

 be given involves, in some form or other, a continuous 

 medium connecting the discrete and separated particles 

 or aioms of matter. 



When a steel spring is bent or distorted, what is it 

 that is really strained? Not the atoms — the atoms arc 

 onlv displaced ; it is the connecting links that are strained 

 — the connecting medium — the jether. Distortion of a 

 spring is really distortion of the aether. All stress exists 

 in the aether. Matter can only be moved. Contact does 

 not exist between the atoms of matter as we know them ; 

 it is doubtful if a piece of matter ever touches another 

 piece, any more than a comet touches the sun when it 

 appears to rebound from it ; but the atoms are connected, 

 as the comet and the sun are connected, by a continuous 

 plenum without break or discontinuity of any kind. 

 Matter acts on matter only through the ^ther. But 

 whether matter is a thing utterly distinct and separate 

 from the aether, or whether it is a specifically modified 

 portion of it-^modified in such a way as to be susceptible 

 of locomotion, and yet continuous with all the rest of the 

 aither, which can be said to extend everywher*e — far beyond 

 the bounds of the modified and tangible portion — are ques- 

 tions demanding, and I may say in process of receiving, 

 answers. 



Every such answer involves some view of the universal 

 and possibly infinite uniform omnipresent connecting 

 medium, the aither of space. 



It has been said, somewhat sarcastically, that the 

 a?ther was made in England. The statement is only an 

 exaggeration of the truth. I might even urge that it has 

 been largely constructed in the Royal Institution, for I 

 will remind you now of the chief lines of evidence on 

 which its existence is believed in, and our knowledge of 

 it is based. First of all, Newton recognised the need 

 of a medium for explaining gravitation. In his " Optical 

 Queries " he shows that if the pressure of this medium 

 is less in the neighbourhood of dense bodies than at great 

 distances from them, dense bodies will be driven towards 

 each other, and that if the diminution of pressure is in- 

 versely as the distance from the dense body, the law will 

 be that of gravitation. 



.•\ll that is required, therefore, to explain gravity is a 

 diminution of pressure, or increase of tension, caused by 

 the formation of a matter unit — that is to sav, of an 

 electron or corpuscle ; and although we do not yet know 

 what an electron is — whether it be a strain centre, or 

 what kind of singularity in the ^ther it mav be — there 

 is no difliculty in supposing that a slight, almost in- 

 finitesimal strain or attempted rarefaction should be pro- 

 duced in the ;ether wh-never an electron came into being, 

 10 be relaxed again only on its resolution and destruction, 

 •strictly speaking, it is not a real strain, but only a 

 " stress," since there can be no actual yield, but onlv a 

 pull or tension, extending in all directions towards infinity. 



NO. 2046, VOL. 79] 



The tension required per unit of matter is almost 

 ludicrously small, and yet in the aggregate, near such a 

 body as a planet, it becomes enormous. 



Ihe force with which the moon is held in its orbit would 

 be great enough to tear asunder a steel rod four hundred 

 miles thick, with a tenacity of thirty tons per square inch, 

 so that if the moon and earth were connected by steel 

 instead of by gravity, a forest of pillars would be neces- 

 sary to whirl the system once a month round their common 

 centre of gravity. Such a force necessarily implies 

 enormous tension or pressure in the medium. Maxwell 

 calculates that the gravitational stress near the earth, 

 which we must suppose to exist in the invisible medium, 

 is 3000 times greater than what the strongest steel could 

 stand, and near the sun it should be 2500 times as great 

 as that. 



The question has arisen in my mind whether, if the 

 whole sensible universe — estimated by Lord Kelvin as 

 equivalent to about a thousand million suns — were all con- 

 centrated in one body of specifiable density,' the stress 

 would not be so great as to produce a tendency towards 

 ethereal disruption, which would result in a disintegrating 

 explosion and a scattering of the particles once more as 

 an enormous nebula and other fragments into the depths 

 of space ; for the tension would be a maximum in the 

 interior of such a mass, and, if it rose to the value 

 10'' dynes per square centimetre, something would have 

 to happen. I do not suppose that this can be the reason, 

 but one would think there must be some reason for the 

 scattered condition of gravitative matter. 



Too little is known, however, about the mechanism of 

 gravitation to enable us to adduce it as the strongest 

 argument in support of the existence of an jether. The 

 oldest valid and conclusive requisition of an ethereal 

 medium depends on the wave theory of light, one of the 

 founders of which was your professor of natural philo- 

 sophy at the beginning' of last century, Dr. Thomas 

 \'oung. 



.\'o ordinary matter is capable of transmitting the un- 

 dulations or tremors that we call light. The speed at 

 which they go, the kind of undulation, and the facility 

 with which they go through vacuum forbid this. 



So clearly and universally has it been perceived that 

 waves must be waves of something — something distinct 

 from ordinary matter — that Lord Salisbury, in his presi- 

 dential address to the British Association at Oxford, 

 criticised the a'ther as little more than a nominative 

 case to the verb to undulate. It is truly that, though it 

 is also truly more than that ; but to illustrate that 

 luminiferous aspect of it, I will quote a paragraph from 

 that lecture of Clerk Maxwell's to which I have already 

 alluded :— 



" The vast interplanetary and interstellar regions will 

 no longer be regarded as waste places in the universe, 

 which the Creator has not seen fit to fill with the symbols 

 of the manifold order of His kingdom. We shall find 

 them to be already full of this wonderful medium ; so 

 full, that no human power can remove it from the smallest 

 portion of space, or produce the slightest flaw in its 

 infinite continuity. It extends unbroken from star to star; 

 and when a molecule of hydrogen vibrates in the Dog- 

 star, the medium receives the impulses of these vibrations, 

 and after carrying them in its immense bosom for several 

 years, delivers them, in due course, regular order, and 

 full tale, into the spectroscope of Mr. Huggins, at Tulse 

 Hill." (It is pleasant to remember that those veteran 

 investigators Sir William and Ladv Huggins are still at 

 work.) 



This will suffice to emphasise the fact that the eye is 

 truly an ethereal sense-organ — the only one which we 

 possess, the only mode by which the EEther is enabled 

 to appeal to us, and that the detection of tremors in this 

 medium — the perception of the direction in which they 

 go, and some inference as to the quality of the object 

 which has emitted them — cover all that we mean by 

 "sight" and "seeing." 



I pass, then, to .another function, the electric and mag- 

 netic phenomena displayed by the sther, and on this I 

 will only permit myself a very short quotation from the 



1 On doins t'-e Arithmetic, 1<owever, 1 find the nec'^'i'ary cor.centratioa 

 absurdly great, showing that such a ma-^s is quite insufficient. 



