550 



NA TURE 



[April 4, 1895 



SOCIETIES AND ACADE\fIES. 



London. 



Royal Society, March 21. — "A possible Explanation of 

 the two fold Spectra of Oxygen and Nitrogen." By E. C. 

 C. Baly. 



The two spectra of oxygen are shown to be of a different 

 nature. They behave diffi?renily, and reasons are given for 

 their being in all probability the spectra of different gases. 

 They may either be two spectra produced by different vibrations 

 of the oxygen molecule, or they may be the spectra of two 

 different modifications of oxygen, or the spectra of two distinct 

 gases resulting fiom a dissociation of oxygen, a combination of 

 which is called oxygen. 



It appeared worth while to undertake experiments with a 

 view of testing the last of these. Oxygen was sparked in an 

 apparatus similar to that used by Prol. J. J. Thomson in his 

 experiments on the elecirolysis of stea^n. Hollow plaiinum 

 electrodes were used, each one of which was connected with a 

 Sprergel irercury pump. In the first experiments, the distance 

 between the electrodes was 35 mm., and the highest pressure 

 compaiible with the appearance of the two spectra was made 

 the starting point of the experiments. In these first experi- 

 ments it was 3S0 mm. The density of the oxygen before spark- 

 ing was deermined, and taken as a test of its purity. The 

 fractions obtained from the anorie and cathode were weighed, 

 and the results are given. They (ill )w the lines ol J. J. 

 Thomson's results, inasmuch as with long sparks a lighter 

 fraction was obtained at the cathode, and with short sparks a 

 heavier fraction. The fractions from the anode were not so 

 definite as from the cathode, though ihe difference was in the 

 right direction. The probable maximum eiror of weighing 

 was o 0001 gram. This meant exactly one in the second 

 decimal place of the density obtained. The general accuracy 

 of the results may be gauged from the densities of unsparked 

 oxygen obtained. 



Density of Density of Density of 



cathode fraction oxyg-n cathode fraction 



with long sparks. unsi arked. with short sparks. 



15 78 ... 15 88 ... 16 00 



15 79 ... 15 87 ... I6-OI 



1580 ... iS'Sg ... 1602 



1579 ... 15 88 ... 16 04 



1588 ... i6o5 



16 05 



Mean of results of other observers ~ 15 887. 



Density of cathode fraction from oxygen, previously for three 

 days fractionated with ihort sparks, 1575. 

 The experiments are still in progress. 



Physical Society, March 22. — Mr. R. T. Glazebrook, 

 F. R. .S., in the chair. — On the objective realiiy of combination 

 tones, by Prof. A. \V. Riickcr and Mr. E. Eilser. The question 

 as to the ohjeciive or subje.tive nature of combination tones 

 has excited much keen controversy, and iheau hors have devised 

 some experiments to elucidate this point. These experiments, 

 some ol which were exhibited before the Society, show that 

 noder certain conditions diHerence and summation tones are 

 produced which are capable o' disturbing resonating bodies. 

 As resonator they have, in ihe first instance, employed a tuning- 

 fork. A piece of thin wood, about 5 in. square, is attached to 

 one of the prongs of this fork, «hile a silvered glass mirror is 

 attached to the other, and the pitth of the fork is very ac- 

 curately adjusted to sixty-four complete vibrations per second. 

 lo Older to detect any movement due to resonance set up in ihis 

 fork, the mirror earned by the prong forms pait of a system of 

 mirrors for protlucing Miclu Ivm's interference bands. By ihis 

 means a movement of the iiron^s cif the fork of 1/8.^1,000 of an 

 inch (half a wavelcngih ol linht; is shown by the dis.ippearancc 

 of the interference binds. As a source of sound a siren w.is 

 employed, this beii'g one of the instruments which Ilelmhullz 

 recommend! as giving the best results. The pitch of the nolcs 

 given by the siren was adjusted by noting the disappearance of 

 the beats produced by one ol the notes with a bowed fork, or 

 by a .stroboicopic method. A la'gc wooden cone, placed be- 

 tween the siren and the resinating fork, served In concentrate 

 the sound on the wooden disc atiachcd lo ths latter. The sen- 

 sitivcnets of the arrangement is such, that when a large Kcienig 

 standard fr.rk, giving sixty-four vilir^tions per second, is struck 

 so lightly that an observer, with his ear close to the fork, cannot 

 detect the fundamental note, the bands instantly disappear. 



NO. 1327, VOL. 51] 



The apparatus, however, is unafTecled by any other note, except 

 one of sixty-four vibrations per second. A number of experi- 

 ments have been made, using various rows of holes on the siren, 

 and in every case when the summation or difference tone corre- 

 sponded to sixty-four vibrations per second, the interference 

 bands vanished, showing that under the conditions of the experi- 

 ment these tones have an objective existence. An experiment has 

 also been made to determine whether Kiienig's lower beat tone 

 when the interval is greater than an octave is objective. In this 

 case, however, the authors entirely failed to get any evidence of 

 such an objective existence. A numberof experiments have been 

 made with a view to elucidating the cause of the pioduciion of 

 the summation tone, which tend to show that it is not the 

 difference tone of the parlials of the fundamental notes. In 

 addition to using a luning-lork to detect the combination tones, 

 the authors have made use of an instrument originally devised 

 by Lord Rayleigh. A light mirror is suspended t>y means of a 

 fine quartz fibre, and hangs in the neck of a resonator, tuned to 

 the given note, and when at rest is inclined at 45° to the axis 

 of the resonator. Under these circumstances, when the resonator 

 responds the mirror tends to turn and set itself at right angles 

 10 the direcion of mo'ion of the air in the resonator. The 

 results obtained with this instrument are in complete accord 

 with those obtained by ilie first method. Up to the present the 

 authors have failed to obtain any evidence of the otijeciive reality 

 of the combination tones produced by organ-pipes and tuning- 

 forks (see p. 474). The discussion on this paper was postponed 

 till after the reading of the next paper. — Some acoustical experi- 

 ments, by Dr. C. V. Burton. (1) On the subjective lowering 

 of pi ch of a note. The author has noticed that if a tuning- 

 fork, mounted on a resonator, is strongly bowed, then if the ear 

 is placed near the opening of the resonator the pitch of the note 

 heard appears lower than when the fork is bowed very gently 

 or is held at some distance. This subjective lowering of pitch 

 is most marked with forks of low pitch ; and in the case of a 

 fork giving a note of 12S complete vibraiions per second, 

 amounts to about a minor third. The author suggests an ex- 

 planation depending on the supposition that the basilar 

 membr.ine of the ear behaves as if it consisted of a number of 

 stretched strings of various lengths, e.ach resounding to a given 

 note ; and that the appreciation of the pitch of a note 

 depends on the localisation of the part of the basilar 

 membrane which resounds most strongly. Further, he 

 shows that in the case of a stretched string, for finite 

 displacements, the siring which most strongly resounds 

 to any noie will have a " natural " period longer than the 

 period of the di-lurbance; the greater the distuibince the longer 

 will be the natural period of the strings most strongly affected. 

 Hence when the intensity of a note increases, the tract of the 

 basilar membrane most strongly affecled is displaced in the 

 direction «hich corresponds to the percefition of lower notes. 

 (2) Objeciivedcm nstra'ion of com'iination tones. Whire two 

 organ-pipes are sounded and alternately separ.ated ami brought 

 close together, an observer, at some distance, hears the did'erence 

 tone much more clearly when the pipes are close together than 

 he does when they are separate. As the position of the pipes 

 with reference to his ear does not appreciably change, the change 

 in the intensity of the combination tone indicates that it has a 

 real objective exis'ence. The author mentioned that ho had 

 sounded his two pipes, which give a diflereiice tone of 64 vibra- 

 tions per second, lefore the collector of Piof. Riiiker and Mr. 

 Edser's app.iratus, but without obtaining any nioti n of the 

 interference bands, and that he was therefore less conlident of 

 the correctness of his deductions than he h.ad been before. Mr. 

 Ed-er menliored thai Dr. Burton had suggested an cx|.|Anation 

 of the production of objective tones in the case of the siicn, which 

 depends on the production of the tones in the wind-chest of 

 the instrument itself when two rows of holes are simulla- 

 neouly opened. They had made an experiment which seemed 

 lo show ihat the above explanation was incorreci, for on con- 

 necting together the wind-ches's of two sirens, fixed on Ihe same 

 spndle, by means of a .short length ol wide me'al tubing, no 

 effect was obseivcd on ihe bands «hen Ihe two noes were 

 produced on different instruments having what was p.aciically 

 a common win l-chesl. — Prof. Everett (communicaierl) said be 

 considered the experimcnis described in the paper proved con- 

 clusively the objec'ivc existence of the suinnianon tones as 

 dis inguished from siippo cd beat tones. He had lately been 

 invesligalin.; Ihe pilch nf ihe loudest combination tone obtained 

 when two notes having fiequencies as 3 to 5 are sounded. Is 



