Septembee 26, 1913] 



SCIENCE 



419 



permeance, its apparently infinite extent, 

 its definite and perfect properties, make 

 the ether the most interesting as it is by 

 far the largest and most fundamental in- 

 gredient in the material cosmos. 



As Sir J. J. Thomson said at Winnipeg : 



The ether is not a fantastic creation of the 

 speculative philosopher; it is as essential to us as 

 the air we breathe. . . . The study of this all- 

 pervading substance is perhaps the most fasci- 

 nating and important duty of the physicist. 



Matter it is not, but material it is; it 

 belongs to the material universe and is to 

 be investigated by ordinary methods. But 

 to say this is by no means to deny that it 

 may have mental and spiritual functions 

 to subserve in some other order of exist- 

 ence, as matter has in this. 



The ether of space is at least the great 

 engine of continuity. It may be much 

 more, for without it there could hardly be 

 a material universe at all. Certainly, how- 

 ever, it is essential to continuity; it is the 

 one all-permeating substance that binds the 

 whole of the particles of matter together. 

 It is the uniting and binding medium with- 

 out which, if matter could exist at all, it 

 could exist only as chaotic and isolated 

 fragments: and it is the universal medium 

 of communication between worlds and par- 

 ticles. And yet it is possible for people to 

 deny its existence, because it is unrelated 

 to any of our senses, except sight — and to 

 that only in an indirect and not easily 

 recognized fashion. 



To illustrate the thorough way in which 

 we may be unable to detect what is around 

 us unless it has some link or bond which 

 enables it to make appeal, let me make 

 another quotation from Sir J. J. Thomson 's 

 address at Winnipeg in 1909. He is lead- 

 ing up to the fact that even single atoms, 

 provided they are fully electrified with the 

 proper atomic charge, can be detected by 

 certain delicate instruments — their field of 



force bringing them within our ken — 

 whereas a whole crowd of unelectrified ones 

 would escape observation. 



The smallest quantity of unelectrified matter 

 ever detected is probably that of neon, one of the 

 inert gases of the atmosphere. Professor Strutt 

 has shown that the amount of neon in 1/20 of a 

 cubic centimeter of the air at ordinary pressures 

 can be detected by the spectroscope; Sir William 

 Eamsay estimates that the neon in the air only 

 amounts to one part of neon in 100,000 parts of 

 air, so that the neon in 1/20 of a cubic centimeter 

 of air would only occupy at atmospheric pressure 

 a volume of half a millionth of a cubic centimeter. 

 When stated in this form the quantity seems ex- 

 ceedingly small, but in this small volume there are 

 about ten million million molecules. Now the pop- 

 ulation of the earth is estimated at about fifteen 

 hundred millions, so that the smallest number of 

 molecules of neon we can identify is about 7,000 

 times the population of the earth. In other words, 

 if we had no better test for the existence of a man 

 than we have for that of an unelectrified molecule 

 we should come to the conclusion that the earth is 

 uninhabited. 



The parable is a striking one, for on 

 these lines it might legitimately be eon- 

 tended that we have no right to say posi- 

 tively that even space is uninhabited. All 

 we can safely say is that we have no means 

 of detecting the existence of non-planetary 

 immaterial dwellers, and that unless they 

 have some link or bond with the material 

 they must always be physically beyond our 

 ken. We may, therefore, for practical 

 purposes legitimately treat them as non- 

 existent until such link is discovered, but 

 we should not dogmatize about them. 

 True agnosticism is legitimate, but not the 

 dogmatic and positive and gnostic variety. 



For I hold that science is incompetent to 

 make comprehensive denials, even about 

 the ether, and that it goes wrong when it 

 makes the attempt. Science should not 

 deal in negations: it is strong in affirma- 

 tions, but nothing based on abstraction 

 ought to presume to deny outside its own 

 region. It often happens that things ab- 



