January 19, 1922] 



NATURE 



75 



suitable ; their discrepancy is wiped out by small 

 variation of air density or height of flight. 



The practical airman will pay no heed to Mr. A. R. 

 Low's elaborate explanation of the units employed in 

 absolute measure (Nature, January 5, p. 12). 

 He has no use for poundal or slug units — fearful 

 traps for the unwary and cause of great confusion of 

 thought — and with the conceit to imagine they will 

 pass current in the whole cosmos. But the rigour 

 claimed for them is beginning to crack and show 

 flaws under the merciless scrutiny of . the new rela- 

 tivity. 



Mr. Low is here coming to the rescue of the un- 

 happy examinee, at the mercy of the whim of the 

 examiner's text-book, and of the rigour demanded 

 for the language employed there, ignored by the 

 practical airman. 



Divergence of language is never to disappear, as 

 it seems, between science and engineering. The 

 engineer refuses to budge when he finds he can arrive 

 at a correct result in practice, and he ignores the 

 rigour prescribed in the examiner's text-book as some- 

 thing to be thrown at the head of the examinee in 

 his conqtiSte des dipldmes. G. Greenhill. 



Staple Inn, January 9. 



Space and >Ether. 



The relation of space and aether has been a subject 

 of controversy. Three-dimensional absolute space has 

 been regarded, before Einstein, as filled with a sub- 

 stantial aether. It is unnecessary to conceive the four- 

 dimensional space-time of the relativists as so filled. 

 If space-time is empty, is space also empty? 



It seems to me that the crux of the difficulty is a 

 wrong assumption that space-time is four-dimensional. 

 Space-time is neither four-dimensional nor three- 

 dimensional, but is two-dimensional. The orthodox 

 analysis of the objective world down to the three 

 fundamental entities of matter, space, and time has 

 been incomplete. That which we call space also in- 

 volves time. That which we call matter also involves 

 both space and time. Thus what we call matter, 

 space, and time should further be analysed as matter- 

 space-time, space-time, and time where matter, space, 

 and time with their new signification are fundamental 

 entities. It is in this new sense that I shall use them 

 hereafter. 



^4i:ther is the synthesis of space-times. It is matter- 

 space-time. A synthesis is a petrified motion. We 

 do not perceive the motion of aether because it is 

 petrified. The motion in a space-time is independent 

 of motion from space-time to space-time along the 

 string that is aether. The so-called velocity of aether 

 is not a change of space, but a change of matter. 



/Ether, being matter-space-time, partakes of the 

 nature of all three. It has the density of matter, the 

 rigidity of space, and the motion of time. 



.^ther is matter-space-time of no mind. The syn- 

 thesis of niatter-space-times of observing minds may 

 be called hyper-aether — filling an absolute four-dimen- 

 sional universe. RelafiyiqlY, to matter, aether is abso- 

 lute. Relatively to mind, hyper-aether is absolute. 

 The real is neither relative nor absolute, but is rela- 

 tivelv absolute. 



Einstein found that space-time was four-dimensional 

 and that the universe was four-dimensional, and 

 therefore argued that space-time was the universe. 

 Therein lies his fallacv. His space-time is the two- 

 dimensional section of a four-dimensional universe. 

 There are two factors in evolution : persistence of 

 identity and change of structure. As space-time is 

 two-dimensional, its identitv persists in the evolution 

 from a three- to a four-dimensional universe. And 



as the world character changes, the internal structure 

 of space-time changes. Einsteinian relativity is an 

 anarchy. It marks a process of revolution, but does 

 not attain a new position of stability. 



Logic is not absolute, but is relative. The laws of 

 logic of an absolute three-dimensional world are not 

 the same as those of an absolute four-dimensional 

 world. To study an absolute four-dimensional world we 

 need a new logic, a new arithmetic, a new geometrv, a 

 new mechanics, and also a new science dealing not only 

 with time as arithmetic does, not only with space as geo- 

 metry does, not only with matter as mechanics does, 

 but also with mind. On the recognition that time, 

 space, matter, and mind contribute each a dimension 

 to the universe I have been able to base an analytical 

 geometry of the universe. 

 _ Space, in the sense of the arena of the three-dimen- 

 sional universe, is matter-space-time, and may be re- 

 garded as filled with aether. The Euclido-Newtonian 

 space-time and the Einsteinian space-time are non- 

 material. But the latter is a stage of travail for the 

 evolution of the former into a space-time with a new 

 internal structure. The claim of the relativists to have 

 demolished Euclid and Newton argues a want of the 

 sense of historic perspective. Man does not progress 

 by demolishing, but by building on, his past. 



S. V. Ramamurtv. 

 Trinity College, Cambridge, January 5. 



Anisotropy of Molecules. 



Direct evidence that the molecules of gases are not 

 spherically symmetrical and are anisotropic in their 

 properties is furnished by the recent experiments of 

 Lord Rayleigh, who has shown that the light scattered 

 by molecules is, in general, not completely polarised 

 when observed in a direction transverse to the pencil 

 of light traversing the gas. The method used by 

 Rayleigh, and by those who have repeated the experi- 

 ments establishing this effect is a photographic one, 

 the track of the primary beam of light as viewed through 

 a suitably oriented prism of Iceland spar being re- 

 corded on a plate with long exposures. In view of 

 the great interest of the phenomenon, it occurred to 

 the present writer that it would be worth while to 

 attempt direct visual observation and measurement of 

 its magnitude. The chief obstacle is, of course, the 

 extreme feebleness of the unpolarised part of the 

 transversely scattered light. This has, however, been 

 successfully overcome. By using the strongest pos- 

 sible illumination (sunlight), securing a perfectly black 

 background, and very carefully screening the eye from 

 extraneous light, it has been found possible to detect 

 with dust-free air at atmospheric pressure the non- 

 extinction of the track as seen through a nicol at any 

 orientation. With carbon dioxide the effect is quite 

 conspicuous, and visual determinations of its magnitude 

 have been successfully made by Mr. K. R. Ramanathan 

 working in the present writer's laboratory. 

 _ A very interesting question arises whether it is pos- 

 sible to establish the same effect by observations on 

 the polarisation of skylight. As is well known, there 

 is a marked defect in the polarisation of skylight 

 in a direction removed 90° from the sun, which is, 

 however, in the main, due to dust and condensed 

 water-vapour in the atmosphere and the diffuse light- 

 ing up of the sky by self-illumination and by reflection 

 from the earth's surface. It occurred to me that the 

 elimination of the effects due to these disturbing 

 factors does not present insuperable difficulties. The 

 reflecting power of landscape (about 008 when covered 

 by vegetation) is known, and its effect is therefore 

 calculable. Dust and low-lying mists may be prac- 



NO. 



725, VOL. 109] 



