April 8, 1920] 



NATURE 



171 



An Electronic Theory of Isomerism. 



I HAVE read with considerable interest the sugges- 

 tion of Dr. H. S. Allen in Nature for March i8 that 

 the Langmuir atom could be applied with advantage 

 to the study of organic compounds. Dr. Allen is, how- 

 ever, doubtful if the " cubical atom " of Langmuir will 

 explain the existence of isomerides of the type of the 

 three malic acids, the glutaconic acids, the cinnamic 

 acids, a-, /3-, and 7-sugars, etc. ; and it is certainly 

 difficult to give formulae for the triple linkage on the 

 cubical atom. These difficulties disappear with the 

 Bohr atom (Nature, February 19, p. 661) and the 

 modification of the Langmuir atom proposed by Major 

 A. E. Oxley {ibid., March 25, p. 105). With both 

 theories n and 5 valencies are obtained, and, so far as 

 a qualitative examination of valency in organic 

 chemistry is concerned, it is difficult to decide between 

 the two models. Major Oxley has, however, shown 

 that his theory can give an adequate explanation of 

 the magnetic properties of organic compounds, and 

 equal success may be obtained with a theory of optical 

 activity. 



The crucial test appears to lie in the calculation of 

 the optical activity of substances in the crystal form, 

 for it is probable that in the liquid condition a large 

 number of isomeric forms exist. 



The alterations in optical activity which occur with 

 change of solvent and the phenomena of muta- 

 rotation and of racemisation appear to be connected 

 with changes in the direction of rotation of electrons. 

 These changes could, perhaps, be more easily ex- 

 plained by the small orbital motions demanded by the 

 T^angmuir theory than by the larger orbital motions 

 in the theory of Bohr. W. E. Garner. 



LTniversity College, London. 



In view of Dr. A. E. Oxley's remarks in Nature 

 of March 25, I should like to point out that the 

 object of my letter was to inquire whether the sup- 

 position of stationary electrons is essential to Lang- 

 muir's theory. Langmuir himself expressed the hope 

 that it would be possible to reconcile his theory with 

 that of Bohr, "which has had such marked success 

 in explaining, and even in predicting, new facts." I 

 ventured to suggest that electrons revolving round the 

 nucleus could form stable groups as required bv 

 Langmuir without needing to be stationary. 



The diflRcultv of explaining- diamagnetism on the 

 theory of the astronomical atom is well known. Possibly 

 the difficulty may disappear when the nucleus is better 

 understood. If electrons are considered as point- 

 charges, the supposition that they revolve in verv 

 small orbits without any constraining force seems 

 arbitrary. Dr. Allen's theory of ring electrons is 

 preferable, and undoubtedly removes certain difficul- 

 ties. It appears, however, that to account for spectral 

 lines the diameter of the orbits must be comparable 

 with that of the atom, which implies that the electrons 

 revolve round the nucleus. 



Since the structure of the atom is still uncertain, 

 would it not be preferable to avoid, if possible, in a 

 chemical theorv a statement as to the immobilitv of 

 the electron";? S. C. Bradford. 



Science Museum, South Kensington, S.W.7. 



Percussion-Figures. 



C. V. gAMAN describes in Nature of October 9, 

 19 19, percussion figures in isotropic solids. These 

 figures are known in geology, and are found on 

 rounded boulders of compact', homogeneous rocks, 

 such as flint and quartzite. Albert Heim ' described 

 in 1871 the " percussion-cones " (Schlagconus) brought 

 forth artificially on pieces of flint by a powerful short 



» Vierteljahrsch-i/t der yaiur/. Ce^e/lscha/t i» Zurich, 1871, p. 140. 



NO. 2632, VOL. 105] 



blow with a hammer. F, Muhlberg,' of Aarau 

 (Switzerland) was perhaps the first geologist who 

 described the percussion-figures (Schlagfiguren) on 

 rounded boulders (1885). On some of the quartz- 

 boulders from the River Aar, near Aarau, he found 

 from hundreds to thousands of circular cracks, which 

 he explained by the abrasion of boulders which for- 

 merly received coniform cracks through the numerous 

 impacts during- their transport through the river-bed. 



These percussion-figures must be intersecting figures 

 of cones and the surface of the boulder, and, there- 

 fore, will form, on sufficiently great boulders, nearly 

 circles, ellipses, and parabolas. Miihlberg described 

 thus percussion-figures arising from torrent-action, 

 whereas A. Bigot' (1907) emphasised that the "figures 

 de percussion " arise from wave-action. He noticed 

 them on the beaches of Basse-Normandie, particu- 

 larly on quartzite boulders. Finally, P. N. Peach* 

 (1912) gave a very fine picture of the "bulbs of per- 

 cussion " found on a rounded stone (chalk flint) 

 dredged by the Michel Sars about 230 miles south- 

 west of Mizen Head, Ireland. He pointed out that 

 these figures indicate that " the stones had originally 

 been dashed. against each other bv torrent- or wave- 

 action." 



Besides the term above-mentioned, Peach also uses 

 the term "chatter marks," which seems to me less 

 commendable, because this expression is also used by 

 T. C. Chamberlin " for a special type of glacial striae 

 on the rock-bed. These curved figTjres were also 

 described by Hagenbach in 1883, and afterwards called 

 "arcs de Hagenbach" by L. Rollier.* 



Batavia, Java, February 11. B. G. Escher. 



A Peculiar Halo. 



On March 16 I observed a peculiar halo here; its 

 form is best shown by a rough sketch. The angles 

 were taken with a pocket slide-rule held at arm's 

 length, and are, therefore, only approximations, but 

 the relative values are probably fairly correct. The 

 halo was brightest at the point above the sun, and 

 faded off somewhat on each side ; it ended rather 

 abruptly at the points shown in the sketch. The 



colours, with red nearest the sun, were not very pure, 

 but they were purer in the arms than in the centre. 

 The phenomenon was visible from 14.45 to i;.4o, 

 with intervals of disappearance when a sheet of alto- 

 stratus became so thick that nothing could be seen 

 through it but the glare of the sun. It was not 

 possible to see any higher layer of cloud, but the hnlo 

 probably had its origin in a layer of cirro-stratus. 

 The measurements were taken at 15.40; a few 

 minutes later the halo disappeared for the last time. 



C. J. P. Cave. 

 Sherwood, Newton St. Cyres, Devon, 

 March 20. 



2 Programm der Aargauischen KantonichuU, Aarau, 1885 ; Die 

 hentigen undfrUheren VerhAltttisse der Aare bet Aarau, p. 4. 



3 Bull tin de li Soc. gM. de France. 46 s^rie, tome iv. (1904), p. f98. 



* Proc Roy. Soc, Edin., 1912 ; aUo Murray and .Hjort, '"The Depth of 

 the Ocean," p. 205. 



5 7th Ann. Kept. U.S. Geol. Survey, p. atS. 



« Bu'letin de la Soc. Bel/ortaine d'Emulalien, No. 27, 1908. 



