176 



NATURE 



[February 9, 1922 



which the source itself is drawn out. It is clearly 

 illogical to suggest, as I>r. Hartridge does, that the 

 prism is responsible for the radiant phenomenon in 

 view of the fact that, in its essential features, the 

 effect is observed even bef<5re the introduction of the 

 prism. 



Using a sufficiently intense source of light and a 

 prism of small angle with optically good and clean 

 faces, and making the observat'ons in a dark room, 

 it should be easy for anyone to satisfy himself by 

 simple tests of the kind referred to by Dr. Hartridge 

 that he is in error, and that Brewster's phenomenon 

 really arises from the scattering of light in the eye, 

 the prism merely acting as a dispersive apparatus 

 modifying the colour and disposition of the streamers 

 in the halo surrounding the source. Judging from 

 the statements made in his letter, Dr. Hartridge 

 would appear to have been particularly unfortunate 

 in his choice of experimental conditions. Any notice- 

 able imperfection in the optical surfaces of the prism 

 would, of course, give rise to scattering, rnasking the 

 true phenomenon due to the eye itself. This is indeed 

 clearly suggested in Brewster's own paper. 



A further and absolutely crucial test is also avail- 

 able. In my paper on the scatteri.ig of light in the 

 refractive media of the eye {Phil. Mag., November, 

 19 19, p. 568), I have described the character of the 

 diffraction-halo arising from this cause in considerable 

 detail. With a source of white light the halo shows 

 a radiating fibrous structure and clearly marked 

 alternations of colour and intensity in its outer parts, 

 A monochromatic source, on the other hand, exhibits 

 a halo with a granular structure and a succession of 

 bright and dark rings. These features are explained 

 in mv paper as due to the diffraction of light by cor- 

 puscles of more or less uniform size included within 

 the structure of the eye. On this view we should 

 expect one half of the first diffraction ring outside 

 the central portion of the halo to be partially 

 achromatised on the introduction of the prism and 

 to appear as a detached semi-circular arc lying beyond 

 the violet end of the spectrum and the displaced 

 position of the achromatic centre. No mere imperfec- 

 tions or irregularities in optical surfaces could, on 

 the other hand, give rise to such a phenomenon. 

 Actual trial confirms the expectation from theory and 

 puts its correctness on an unassailable basis, 



C, V, Raman, 



21® Bowbazaar Street, Calcutta, January 4. 



The Naming of the Minor Planet No. 907, Barnardiaiia. 



In Nature for September 8 last (vol. 108, p. 69), 

 at the end of "Our Astronomical Column," attention 

 is directed to the naming by Dr. Max Wolf of two of 

 his asteroids in Astronomische Narhrichten, No. 51 16. 

 They are No. 834, Burnhamia, and No. 907, Bar- 

 nardiana. In commenting on these asteroids Nature 

 infers that they were named after two American astro- 

 nomers. While it is true that Prof. Burnham's 

 memory is thus honoured, Barnardiana was not 

 named after me, but in memory of Mrs. Rhoda Calvert 

 Barnard, who died on May 25, 192 1. This is evident 

 from the following quotation from a letter to me by 

 Dr. Wolf on the subject: — 



"Wenn ich den Vornamen Ihrer Gemahlin gekannt 

 hiitte, und — vorausgesetzt, dass er nicht schon ver- 

 wendet worden ist — wiirde ich ihn einem meiner 

 Planeten zur Erinnerung an Ihre liebe Frau beige- 

 geben haben. Da das nicht ging, so taufe ich den 

 Planeten 907 1918 EU, auf den Namen : Bar- 

 nardiana." 



For some reason No. 5 116 of the Astronomische 

 Nachrichten containing these names has only 

 NO. 2728, VOL. 109] 



very recently reached the Yerkes Observatory. I was 

 unaware until then that it did not distinctly state the 

 planet was named after Mrs. Barnard. Though not 

 actively engaged in astronomical work, in her long 

 life in astronomy she had endeared herself to the 

 many astronomical people she had met by her thought- 

 ful and unselfish interest in them and in their work. 

 Hers was a life of love and sympathy. 1 am grateful 

 to Dr. Wolf for thus perpetuating her memory. 



E. E. Barnard. 

 Yerkes Observatory, University of Chicago, 

 January 11. 



The Resonance Theory of Hearing. 



Dr, Hartridge imputes to me great absurdities 

 which, either in irony or by an excess of courtesy, 

 he terms "slight errors " (Nature, January 19, 

 p, 76). Under (i) he takes my plain words, the 

 result "must always be of the same nature," to mean 

 that the result must always be the same ! Of course, 

 the harmonic analysis of his oboe and flute combina- 

 tion will not give the same result as in the case of 

 violin and cornet, but in both cases the result will be 

 of the same nature, in that there will be only one 

 fundamental tone. If the data supplied to the sen- 

 sorium from the cochlea are simply the result of an 

 harmonic analysis, the two notes must appear to the 

 ear inseparably blended in one note. I have not left 

 binaural audition out of consideration. The ability 

 to distinguish two concurrent notes of the same pitch 

 and different quality seems unaffected by both sources 

 being equidistant from either ear. 



Under (2) Dr. Hartridge should know as well as I 

 know that the pitch of a note depends solely upon 

 the period of its fundamental tone. The example 

 which I proposed eliminates the possibility of beats, 

 the two notes being in perfect physical unison. And, 

 further, since the note made by the teeth is generated 

 by the other note, it cannot be heard except in the 

 combination. Its perception is, therefore, a cogni- 

 tion, not a recognition. At any instant during the 

 production of the two notes (which may be sustained 

 for twenty seconds easily) it is possible to turri the 

 attention to the note made, by the teeth and to hear 

 that its pitch is that of the hummed note. At no 

 instant could the resonators which Dr. Hartridge, 

 outstripping Sir Arthur Keith, " finds " in the cochlea 

 furnish the data for anything but a change in the 

 qualitv and intensity of the hummed note. This 

 objection remains untouched by Dr. Hartridge's 

 animadversions. It goes to the root of the matter, 

 and cannot " fall to the ground " as a superstructure 

 mav. W. Perrett. 



University College, Gower Street, W,C,i, 

 January 26. 



Aurora Borealis of January 30. 



Happening to look out at ii.^olast night I per- 

 ceived a strong auroral glow extending from N. by E. 

 through N. to W. The light was quite bright, and 

 on going into the garden I noticed that my body cast 

 a shadow and that I could read the headlines of the 

 Times quite readily. There were no streamers, but 

 several luminous patches, especially due N., where a 

 blunted cone of greenish light rose vertically up from 

 the horizon to a height of 10°. 



The sky was partially, and later almost totally, 

 covered bv thin clouds, which drifted up from S. 

 under the influence of light airs. The atmosphere was 

 misty and the temperature decidedly warm. 



Charles S, Leaf.^ 



7 Grange Road, Cambridge, January 31, 



