December 9, 1909] 



NA TURE 



'57 



witliin any one of a number of ranges lying in the vicinity 

 of 2/i, 2/1/2, 2/1/3 • • •' where /i is the natural frequency 

 of the system. 



Further investigations upon this and other allied subjects 

 appear in seven subsequent issues of the Philosophical 

 Magazine. As regards the forced oscillations discussed in 

 the Quarterly, the author gives, in the way of experimental 

 verification of his mathematics, the following : — the in- 

 fluence of the disturbing motion becomes feebler as r 

 increases, but it may easily be observed experimentally in 

 a number of cases. For this purpose suspend a load by 

 means of a spiral spring, and attach to it a pendulum 

 light compared with the load, but of such density that 

 the air resistance is negligible ; the pendulum being of 

 suitably chosen period, it will be found that when the load 

 is carefully adjusted the relative equilibrium of the pen- 

 dulum in the vertical motion is unstable. 



I believe the beauty and interest of the results obtained 

 by Mr. Andrew Stephenson have not been generally 

 realised, otherwise it is nearly certain that something more 

 satisfying in the way of experimental demonstration of 

 these oscillations than mere observation of " instability of 

 equilibrium " in certain cases would have been put in the 

 field. 1 think an experimentalist would hardly be pleased 

 with anything less than the actual permanent maintenance 

 of oscillations of the type mentioned, i.e. something similar 

 to the experiments of Faraday, Melde, and Lord Rayleigh 

 for the case of double frequency, which, as Mr. Stephenson 

 points out, is only one particular case of his general 

 theorem. 



During the course of certain acoustical work which I 

 have been engaged in during the last two years, I observed 

 certain types of stationary vibration which I find are un- 

 doubtedly of the kind contemplated in Mr. Stephenson's 

 paper. These observations were made with an apparatus 

 from which any new effects were apparently hardly to be 

 expected. The arrangement was the well-known one of a 

 string maintained in vibration by a tuning-fork oscillating 

 in a direction parallel to the string. It is generally sup- 

 posed that the oscillations permanently maintained have a 

 frequency which is half that of the tuning-fork. I found 

 this was not always the case. With an electrically main- 

 tained tuning-fork the amplitude of oscillation of which 

 could be readily adjusted, the stationary oscillation of the 

 string had a frequency of i of, equal to, 3/2 times, 

 twice, &c., that of the tuning-fork, each term in the 

 harmonic series appearing separately by itself with a fairly 

 large amplitude, or with one or more of the others con- 

 jointly, according to circumstances. The frequency- and 

 phase-relations could be studied by several methods, most 

 of which were very simple applications of the principle of 

 Lissajous's figures. 



The possibility of isolating the harmonics, and also 

 certain serious discrepancies between theory and experi- 

 ment as regards the phase of the oscillations in the case 

 of double frequency, were traced to the existence of varia- 

 tions of tension in free oscillations of sensible amplitude. 

 These variations of tension were experimentally demon- 

 strated by a special form of monochord denominated the 

 " Ectara " (vide the Journal of the Indian Mathematical 

 Club for October, pp. 170-5), in which the sounding surface 

 is a membrane perpendicular to the vibrating string, and 

 emits a tone having twice its frequency. 



Post-Box 59, Rangoon. C. V. Raman. 



Absorption-bands in Colourless Liquids. 

 In the obituary notice of the late Dr. W. J. Russell, 

 F.R.S. (N.iture, November 25, p. loi), whose genial 

 friendship I enjoyed and with whom, when occasionally in 

 London, I had friendly intercourse, it is stated that he 

 had published " papers conjointly with Mr. Lapraik on 

 absorption spectra, and notably one on the absorption bands 

 in the visible spectra of colourless liquids, which was the 

 pioneer paper in a branch of inquiry that has been ably 

 followed up by Prof. Noel Hartley, F.R.S. , Mr. E. C. C. 

 Baly, F.R.S., and others." It seems ungracious to call 

 in question the accuracy of this reference, and I feel, 

 indeed, a great inclination to let it pass without comment, 

 although it is incompatible with authoritative statements 

 made elsewhere; but, inasmuch as the passage is liable 



NO. 2093, VOL. 82] 



to be reprinted without question and repeated in other 

 publications, I consider it would be better to invite the 

 writer's attention to the Chemical Society's Transactions, 

 xxxix., 153-68, 1881, " Researches on the Relation 

 between the Molecular Structure of Carbon Compounds 

 and their Absorption Spectra," and suggest that he should 

 compare it with the paper which follows in the same 

 volume, pp. 168-73, " On 'h^ .Absorption-bands in the 

 Visible Spectrum produced by Certain Colourless Liquids." 

 Having done so, I think he will agree that not only is the 

 latter not the pioneer paper, but also that there is very 

 little in common between the two. In fact, the latter 

 communication is more closely allied to the work of Abney 

 and Festing in the infra-red region, a work to which 

 the authors themselves make a special reference. 



W. N. Hartley. 

 Royal College of Science, Dublin, November 30. 



The Inheritance of /Acquired Characteis. 



In his review of Prof. Poulton's work, " Charles Darwin 

 and the Origin of Species," Prof. Meldola says (Nature, 

 November 25, p. 92) that the Darwinian theory is abso- 

 lutely dependent upon the truth of the belief " in the 

 transmissibility by inheritance of individual differences or 

 ' fluctuations.' " This is undoubtedly true. There is now 

 available a vast amount of evidence tending to show that 

 " fluctuations " seemingly the direct results of changes in 

 the environment are inherited ; but how is it possible to 

 convince Weismann and his followers that such " fluctua- 

 tions " have not been due, as they will say, to " spon- 

 taneous germinal variations "? Surely the onus probandi 

 really rests with them ! 



We have here the question of the inheritance or not of 

 acquired characters reduced to its simplest terms. There 

 is much and very varied evidence to show the influence of 

 changes in the environment in producing *' fluctuations " 

 which are heritable, but what evidence can those who 

 disbelieve in the inheritance of acquired characters present 

 to show that in all such cases there must be a primary 

 germinal change? H. Charlton Bastian. 



The Athenaeum, November 26. 



Luminous Night Clouds and Aurora Spectrum. 



On the evening of Friday, December 3, there occurred 

 a very brilliant display of luminous night clouds in rather 

 peculiar circumstances. During the earlier part of the 

 evening the sky had been clear, and no indications of an 

 aurora were observed. About 10.15 P-ni. the sky became 

 completely overcast quite suddenly, and it was noticed that 

 this appeared to be by general formation of haze in situ, 

 and not by the drifting of clouds. .Almost immediately 

 after this numerous patches of light cloud appeared, 

 travelling with considerable velocity eastward. From 

 numerous previous experiences it was at once apparent that 

 these were not ordinary cloud forms, and the moon was 

 not high enough to account for their extreme brilliancy. 

 Careful examination with a hand spectroscope confirmed 

 the surmise that they were luminous clouds, the green 

 auroral line being very bright and sharply defined ; on 

 several of the brighter masses other lines were suspected, 

 but not sufficiently well to assign any position. These 

 observations were confirmed by Mr. VV. Moss. At about 

 10.45 p.m. the clouds gradually became less frequent, and 

 the sky became clear again almost as suddenly as it had 

 been overcast. 



It will be of interest to hear if any magnetic storm has 

 been recorded for this epoch. The surface of the sun has 

 been in continued disturbance during the past week, as 

 evidenced by the rapidly changing forms of numerous spots. 

 One of the largest groups would be passing round the 

 north-west limb. Charles P. BuTLER. 



Solar Physics Observatory, London, S.W. 



Coloration of Birds' Eggs. 

 Some time ago I wrote a short letter asking for informa- 

 tion about the colours of birds' eggs, which appeared in 

 Nature of May 14, 1908. I read the answer to my letter 

 in a subsequent number of Nature, which, unfortunately, 

 did not appear to me to throw much light on the subject. 



