390 



NATURE 



[May 27, 1920 



bows respectively. The results for i. and 11. are shown 

 in Figs. 3, and 4. It is unquestionable that these 

 curves faithfully represent the phenomenon as we ob- 

 served it, the portions shown with thicker lines being 

 those within the limits of the water, which alone we 

 were able to see. The calculated curve for iii. (not 

 shown) is equally corroborative. The aureole seen 

 round the shadow of the observer's head is consistent 

 with the attribution of the phenomenon to water 

 globules upon a surface (see J. M. Pernter, " Meteoro- 

 logische Optik," 1910, p. 424). 



It is of interest to note that the closed curve is a 

 rainbow inside out, and with the secondary bow 

 within the primary. 



Since writing the above we once again found the 

 bows visible, and a careful examination of them 

 seemed to confirm the conclusions arrived at on every 

 point. On this occasion the film was broken by 

 spaces of clear water, and at these spaces the bow's 

 were interrupted. The space within the inner bow 

 was filled with faint, diffuse lurninosity, and a marked 

 feature was the blackness of the zone between the 

 inner and outer bows. C. O. Bartrum. 



32 Willoughby Road, Hampstead. 



" AII-or-None " in the Auditory Nerve. 



Prof. D. C. Miller ("The Science of Musical 

 Sounds," 1916, p. 184) admits the reality of beat- 

 tones, but says that they are purely subjective, having 

 no physical existence. This seems unsatisfactory. 

 To begin with heats, it is wrong to say that it is 

 the places of maximum intensity which are properly 

 called heats. This is an illusion, due to too familiar 

 diagrams. The maximum of intensity occurs at no 

 place, but at a point of time which, at its own 

 instant, the maximum not being absolute, is not 

 impressive. At any point of time the next vibration 

 of a sound may be of greater amplitude or it may 

 not, and the listening ear, being unable to foretell, 

 cannot tell us in the present when the maximum is 

 attained. The perception of a maximum is bound to 

 arrive, in fact, the day after the fair, when the sound 

 is on the wane. On the contrary, it is the minimum 

 of intensity which gives the effect of the beat." This 

 is clear if the two primary tones are of equal ampli- 

 tude and there is a phase of silence, when the differ- 

 ence of sensation is a difference, not of degree, but 

 of "kind. It has been shown that if a musical note 

 is suddenly reduced to silence, the interruption of the 

 series of vibrations restores the last of the series of 

 periodic impulses to its isolated value ; the note ends 

 with a kind of shock or tap, comparable to one of a 

 series of hard beats. If periodic beats are rapid 

 enough, the final impulses at the interruptions form 

 a fresh series, and are free to evoke in the sensorium 

 a sensation of tone of the same frequency as the 

 beats, a beat-tone ; and this is best observed when 

 the beats are not too violent. 



Beat-tones are, therefore, no more subjective and 

 have no less phvsical existence — although they may 

 have been invisible hitherto in tracings and photo- 

 graphs — than any other real tone; and since both 

 beat-tones, ^-q and iq-^, are best heard, at least with 

 intervals less than an octave, when the primaries are 

 not powerful, there never has been a good reason for 

 rejecting Young's view of their origin, nor for ascrib- 

 ing to Koenig the discovery of those "upper" beat- 

 tones which were discussed by Young before the 

 Royal Society in 1800. (In Faraday's copy of the 1807 

 quarto there is a book-mark at p. 5^4 of vol. ii., 

 perhaps indicating that the chapter on the coalescence 

 of musical sounds has more than an historical in- 

 terest.) 



But beats are nroduced bv primaries of unequal 

 NO. 2639, VOL. 105] 



amplitude, and in such cases there is no phase of 

 silence, and apparently no absolute minimum of 

 intensity. Here we have something comparable to 

 the first d in "would do " rather than the first t in 

 "not too," to a voiced rather than a voiceless occlu- 

 sive. If in the physiology of hearing we assume 

 similarity of character in the nervous impulse to that 

 which is established for motor nerves, the contribution 

 of a single nerve-fibre, not being greater than the 

 faintest sound audible in a sound-proof room, is in 

 ordinary circumstances imperceptible ; ^in the fluctua- 

 ting intensity of a beating note many fibres will be 

 implicated at the maximum ; at the minimum, rela- 

 tively few. At a minimum of intensity which is not 

 absolute some fibres will continue to conduct the 

 series of impulses of the note, while others will at 

 this instant discontinue, and the impulse preceding 

 the interruption may evoke the displeasing sensation 

 of a noise, whereas with slow beats, where the dis- 

 continuity in many fibres is spread over a longer time, 

 the effect is not so, but pleasant. Hence with two 

 primaries of nearlv the same frequency we may hear 

 at the same time beats and the beating note. When 

 the interval between the primaries is sufficient for 

 the frequency of the beats to be that of a real tone, 

 we may in the same manner hear at the same time 

 the separate primaries and either the beats or the 

 beat-tone, or both the beats and 'the beat-tone. 

 Further application of this principle will be found to 

 offer a solution of other obscure problems in hearing. 



W. Perrett. 

 University College, Gower Street, May 20. 



British and Foreign Scientific Apparatus. 



My attention has been directed to a letter ap- 

 pearing in the issue of Nature for May 6 dealing 

 with the subject of scientific apparatus. Your cor- 

 respondents are extremely moderate in tone, but they 

 do not state the class of apparatus to which they 

 are referring. 



Members of the association of which I have the 

 honour to be chairman manufacture a large number 

 of scientific apparatus, not only in glass and porce- 

 lain, but also other goods as well. Some of these 

 were manufacturers in this country before the war, 

 and proved by the quality of their products that they 

 were able to stand against foreign competition ; other 

 members have entered the scientific trade only since 

 the outbreak of the war, mainly at the request of 

 the Government. The difficulties they have experi- 

 enced have been extremely great, but they can 

 prove that the quality of most glassware articles 

 turned out is equal in many respects to that of 

 articles previously imported from abroad. 



Certain complaints have reached us ; these have 

 been most carefully investigated, and in many cases 

 we found that the complaint dealt with glassware 

 which was not manufactured by our members, but 

 had been sold without any mark or badge of the 

 manufacturer. Our members will be only too 

 pleased to co-operate in every possible wav with 

 scientific workers, and look to them for the help 

 necessarv in establishing this "key" industry and 

 placing it on a thoroughly sound basis. 



As regards State aid, we do not want this in the 

 form suggested, but rather we desire the creation of 

 some method by means of prohibition whereby the 

 industry will be enabled to establish itself, and at 

 the same time the customer will not be penalised by 

 being unable to sjet his material or the quantitv of 

 apparatus he desires. Under the form of prohibition 

 which has been suggested, all orders for apparatus from 

 abroad would have to come before a Special Com- 

 mittee of the Board of Trade. This Committee would 



