62 Sir Oliver Lodge [Feb. 21, 



concomitant 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 the expense of corresponding move- 

 ment in another, withont any similar kind of transmission or material 

 connection 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 l)e 

 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 

 connexion is obvious, the explanation is not coniplete : for 

 when the mechanism of attraction is understood, it will be found 

 that a l)ody really only moves because it is pushed by something 

 from behind. The essential force in nature is the vis a tergo. 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 

 requiring explanation ; and the only explanation that can be given 

 involves, in some form or other, a continuous medium connecting the 

 discrete and separated particles or atoms of matter. 



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

 strained ? Not the atoms— the atoms are only displaced ; it is the 

 connecting hnks that are strained — the connecting medium— the ether. 

 Distortion of a spring is really distortion of the ether. All stress 

 exists in the ether. 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 thi'ough the ether. But whether matter 

 is a thing utterly distinct and separate from the ether, 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 ether, which can be said to extend everywhere — far beyond the 

 bounds of the modified and tangible portion — are questions demand- 

 ing, and I may say in process of receiving, answers. 



Every such aiiswer involves some view of the universal and 

 possibly 'infinite uniform omnipresent connecting medium, the Ether 

 of space. 



It has been said, somewhat sarcastically, that the ether 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 

 un which its existence is beUeved in, an.d- our knowledge of it is 



