7o8 



NATURE 



{August 5, 1920 



primitive plant formation is desecrated by a single 

 foreign invader." The concluding chapters deal 

 with the division of the islands into botanical dis- 

 tricts, and the affinities, origin, and history of the 

 flora. As regards the latter, Dr. Cockayne admits 

 the necessity of great land extension in the Ant- 

 arctic direction. 



Annual Reports on the Progress of Chemistry for 



1919. Issued by the Chemical Society. 



Vol. xvi. Pp. ix + 234. (London: Gurney and 



Jackson, 1920.) Price 4^. 6d. net. 

 One of the most useful of the publications issued 

 by the Chemjcal Society is the annual volume 

 summarising the progress made each year in the 

 various main branches of chemistry. With this 

 bird's-eye view of the year's achievements at com- 

 mand, a worker is readily able to survey, in some- 

 thing like proper perspective, the advances made 

 in other divisions of the science as well as in his 

 own. 



The period covered by the present volume 

 synchronises with the return of many scientific 

 workers from occupations connected more or less 

 directly with the conduct of war to conditions 

 which, in due time, will no doubt lead to a full 

 resumption of scientific investigation for its own 

 sake. Meanwhile it is too early to expect 

 accounts of many such researches. For the 

 moment, the aftermath of war work is being 

 shown in papers dealing with technical problems 

 on which chemists have worked during the last 

 few years. There is, nevertheless, a fair amount 

 of purely scientific research work recorded. 

 Rutherford's investigations on atomic disintegra- 

 tion are of fundamental importance if the results 

 are eventually confirmed ; and other notable pieces 

 of work are the studies on the "poisoning" of 

 palladium as a catalyst by hydrogen sulphide, on 

 the origin of alkaloids from amino-acids, and on 

 fermentation. In the "crystallography" section, 

 it may be noted, a good description is given, with 

 figures, of the principles underlying X-ray 

 methods of exploring crystal structure. 



The Ascent of Man: A Handbook to the Cases 

 illustrating the Structure of Man and the Great 

 Apes. (London County Council.) Pp. 74. 

 (London : The Horniman Museum and Library, 

 n.d.) Price 6d. 

 This little handbook, by Dr. H. S. Harrison, 

 curator of the Horniman Museum, is written in 

 simple language, and admirably suited to stimu- 

 late interest in the recent remarkable progress in 

 our knowledge of the ancestry of man. The biblio- 

 graphy with which it concludes will also be helpful 

 to those who wish to pursue the subject further. 

 Dr. Harrison emphasises the fact that man must 

 be traced back to small arboreal mammals, and 

 well observes: "It is scarcely too much to say 

 that if the earth had borne no trees, there would 

 have been no men." His anatomical descriptions 

 are mad*>. readable and interesting by his frequent 

 references to habits and modes of life. 



A. S. W. 

 NO. 2649, VOL. 105] 



Letters to the Editor. 



[The Editor does not hold himself responsible for opinions 

 expressed by his correspondents. Neither can he undertake to 

 return, or to correspond with the writers of, rejected manu- 

 scripts intended for this or any other part of Nature. No 

 notice is taken of anonymous communications.] 



Relativity and Reality. 



No one would wish to strain at a gnat. If the 

 relativist finds it convenient to make the time-axes of 

 his four-dimensional medium the pure imaginary 

 direction by writing ( = rV'(-i), that would appear to 

 be a matter of indifference, so long as for each co- 

 ordinate a single line or axis still suffices to indicate 

 the values that x, y, z, and r can bear. But the 

 matter becomes complicated as soon as we project in 

 oblique directions. Thus take the equations of the 

 "restricted" relativity theory, 



x = ^(x'-ut'), t = l3it'-ux'), f3 = {i-u')-i. 

 which upon substitution become 



x = l3(x'-iuT'), r = fi{T'+iux'), 

 and these can be written 



x = x' cose-r' sin 6, T = x'sm O+t' cosB. 

 if tan B = iu. 



Thus (x, r) (x', t') are co-ordinates of the same point 

 projected upon different axes, but not in any real 

 direction. According to this system, A can grasp B's 

 scheme of space-time only when he generalises his 

 own x, y, z, r, so that each of them stands for an un- 

 restricted complex variable. But such a removal of 

 restriction cannot be pictured without allotting a 

 whole plane to each variable, and that means doubling 

 our whole apparatus of representation and a descrip- 

 tion of events in terms of not fewer than eight real 

 dimensions. Surely no physicist can be expected to 

 take the system seriously. 



The mathematician does not seem to be aware that 

 he is asking one to swallow a camel. Thus in Prof. 

 Eddington's recent book, "Space, Time, and Gravita- 

 tion,'' we read (p. 48): "The observer's separation 

 of this continuum into space and time consists in 

 slicing it in some direction . . . clearly the slice 

 may be taken in any direction ; there is no question 

 of a true separation and a fictitious separation." 

 But there is the qualification, which surely deserves 

 rnention, that every real direction must be excluded, 

 since the angle is necessarily imaginary, because 

 /3, which is greater than unity, is its cosine. The 

 original passage from (x, t) to (x', f) is real, and we 

 get back to reality by slicing in an imaginary direc- 

 tion with respect to an imaginary axis. The device 

 should be classed with the focoids, those two imaginarv 

 points at infinity .where any two concentric circles 

 touch. They recall to the mathematician's mind 

 certain algebraic forms, but have no other actuality 

 whatever. The point I would make, however, is this : 

 If this analogy is dropped, the idea of time as a 

 fourth dirnension is not in any way advanced by the 

 interpretation of the equations above from the position 

 it has occupied since the days of Lagrange. 



R. A. Sampson. 

 Royal Observatory, Edinburgh, Julv 26. 



An Attempt to Detect the Fizeau Effect in an Electron 

 Stream. 



Without in any way touching the theoretical 

 aspect of the case, it seems worth while to put on 

 record the null result of an experiment to see whether 

 the Fizeau effect was present in the case of a beam 

 of light passing along a rapidly moving stream of 

 electrons. 



A pair of Jamin plates giving a separation of the 



