SPACE AND TIME 179 



appear as real a perception as the air, and the matter is, 

 perhaps, largely one of definition. Still Hertz's experi- 

 ments,^ for example, do not seem to me to have logically- 

 demonstrated the perceptual existence of the ether, but 

 to have immensely increased the validity of the scientific 

 concept, ether, by showing that a wider range of percep- 

 tual experience may be described in terms of it, than had 

 hitherto been demonstrated by experiment. Further, 

 many of the properties which we associate with the ether 

 are not such as our past experience shows us are likely 

 to become matter for direct sense -impression. I shall 

 therefore continue to speak of the ether as a scientific 

 concept on the same footing as geometrical surface and 

 atom. 



S II. — On the General Nature of Scientific Conceptions 



Our discussion of these spacial conceptions will the 

 better have enabled the reader to appreciate the nature of 

 scientific conceptions in general. Geometrical surface, 

 atom, ether, exist only in the human mind, and they are 

 " shorthand " methods of distinguishing, classifying, and 

 resuming phases of sense-impression. They do not exist 

 in or beyond the world of sense-impressions, but are the 

 pure product of our reasoning faculty. The universe is 

 not to be thought of as a real complex of atoms floating 

 in ether, both atom and ether being to us unknowable 

 " things-in-themselves," producing or enforcing upon us 

 the world of sense-impressions. This would indeed be 

 for science to repeat the dogmas of the metaphysicians, 

 the crassest paradoxes of a short-sighted materialism. 

 On the contrary, the scientist postulates nothing of the 

 world beyond sense ; for him the atom and the ether are 

 — like the geometrical surface — modes by aid of which 

 he resumes the world of sense. The ghostly world of 

 " things-in-themselves " behind sense he leaves as a play- 



^ Annalen der Physik, 1887-9. See also Nature, vol. xxxix. pp. 402, 

 450, 547. An interesting account of Hertz's researches by von Tunzelmann 

 will be found in The Electrician for 1888, vol. xxi. pp. 587, 625, 663, 696, 

 725, 757, 788, and vol. xxii. pp. 16, 41. 



