December i, 192 i] 



N^ATURE 



449 



Modified Systems of Extra-nuclear Electrons." The 

 chief point of interest in this work is that by means 

 of a suitable t3-pe of discharge it is possible to obtain 

 from potassium two different spectra which corre- 

 spond closely to the red and blue discharges in argon. 

 Bearing in mind the fact that, according to present- 

 dav views of atomic structure, a potassium atom 

 robbed of its valency electron has an outer electron 

 configuration identical with that of argon, Prof. 

 McLennan 's results are explained if we suppose that 

 it is electrons in this configuration which are respon- 

 sible for the radiations he obtained. 



Two. papers were read by Prof. R. W. Wood, whom 

 the section was fortunate enough to have present in 

 the capacity of foreign guest. In the first of these, " The 

 Time-interval between the Absorption and Emission 

 of Light in Cases of Fluorescence," Prof. Wood 

 described beautiful experiments with a new type of 

 phosphoroscope (capable of recording to 1/400,000 

 second), which proved that mercury vapour illuminated 

 bv the flash of an aluminium spark remains non- 

 luminous for about 1/15,000 second, and then bursts 

 into a flash of green fluorescent light. Nothing but 

 mercurv vapour has as yet exhibited the phenomenon. 

 The vapour must be freshly formed in order that 

 it may fluoresce ; metallic mercury must be present 

 liberating nascent molecules. In his second paper, on 

 "The Spectra of Hydrogen from Long Vacuum 

 Tubes." Prof. Wood described how the use of ven." 

 long discharge tubes enables the pure Balmer spec- 

 trum of hydrogen to be isolated from the continuous 

 secondary spectrum, with the result that twenty lines 

 of the series — as compared with thirt\' in the solar 

 spectrum and but twelve in ordinary laboratory,- ex- 

 hibits — can be recorded. 



Another distinguished foreign guest. Prof. J. C. 

 KaptCATi, read a paper entitled " First Attempt at a 

 ThecM^,- of the Structure and Motion of the Stellar 

 Svstem." In this communication the author gave 

 reasons for supposing that the stars, in the domain 

 where the density exceeds one-hundredth part of 

 'the density near the sun, are distributed so that the 

 surfaces of equal density are rotation ellipsoids all 

 with their axes towards the pole of the Milky Way, 

 and for treating them as in rotatory* motion in two 

 oppositely directed streams about this axis. By treat- 

 ing the whole system statistically according to the 

 kinetic theon,' of gases, results are obtained regard- 

 ing distribution which are in accordance with facts ; 

 and, for the region where star-streaming had originally 

 been observed, the relative velocity of the streams 

 calculated agrees almost perfectly with that observed. 



Other papers presented during the morning were 

 "Tubes of Force in Four-dimensional Physics," by 

 Prof. E. T. Whittaker ; "The Reception of Wireless 

 Waves on a Shielded Frame Aerial," in which Mr. 

 A. A. Campbell Swinton described experiments aim- 

 ing, without success, at the construction of a uni- 

 directional wireless receiver; and cwie entitled " Pre- 

 hensilitv : A Factor of Gaseous Adsorption," bv Prof. 

 H. Briggs. 



The afternoon was devoted to demonstrations and 

 exhibitions. Dr. Carse had arranged an exhibit of 

 historical apparatus, and members of the section also 

 visited Prof. Whittaker '5 mathematical laboratory. 

 Mr. J. J. Dowling gave a demonstration of a record- 

 ing ultramicrometer. based upon the use of thermionic 

 valves. Dr. W. L. Balls showed his simple. harmonic 

 analyser and periodoscope in operation, and Dr. 

 Dawson Turner and Mr. D. M. R. Crombie made 

 -several experiments upon the behaviour of an elec- 

 trified pith ball in an ionised atmosyiAere. The attend- 

 ance throughout the afternoon was large. 



NO. 2718, VOL. 108] 



On September 9 the first item <mi the prc^ramme 

 was Prof. O. W. Richardson's illuminating presi- 

 dential address on "Problems of Physics." The rest 

 of the morning was devoted to a discussion, jomtly 

 with the Chemistry Section, on "The Structure of 

 Molecules," already reported in Nature of 

 October 13 (p. 218). 



More than two hours were spent on the morning 

 of September 12 in discussing "The Quantum 

 Theory." To Mr. C. G. Darwin fell the task of 

 opening this discussion by outlining the theor\- and the 

 experimental results which had necessitated its adop- 

 tion. Sir Oliver Lodge communicated to the discus- 

 sion two notes bv Sir Joseph Larmor (afterwards 

 published in the 'Phil. Mag. for October), entitled 

 •Escapements and Quanta" and "Non-radiating 

 Atoms." In the first it was suggested that perhaps 

 atoms behaved like clocks, in that they possessed 

 large stores of energy, not associated with periodicity, 

 but released in quanta by the periodic orbital elec- 

 trons. In the second note the author gave the condi- 

 tions which must be fulfilled in order that, with close 

 approximation, there should be no radiation from 

 atoms having orbital electrons except when disturbed. 

 Sir Oliver Lodge in his own contribution suggested 

 that the cause of the change of orbit in the Bohr 

 atom might be the absorption of a bombarding elec- 

 tron bv the nucleus, thus reducing the atomic number 

 bv unity and necessitating the emission of energy 

 during the establishment of the new stationary- state. 

 It was admitted that this view involved the trans- 

 mutation of elements, but only to so small a degree 

 that the percentage changed would be inaccessible of 

 obserN'ation. Prof. J. W. Nicholson dealt with the ques- 

 tion of stability' in connection with permissible electron 

 orbits in hydrogen and helium, and examined them 

 from the point of view of magnetic properties and 

 characteristic radiation. The connection between 

 quanta and magnetic induction was explained by Dr. 

 H. S. Allen, the results indicating the existence of 

 discrete tubes of magnetic induction as suggested 

 long ago by Faraday. Prof. W. Wilson gave a 

 general mathematical account of the theon,-, and 

 referred especially to Bohr's principle of analogy, 

 which, although successfully applied to spectra in 

 certain cases, should be regarded as only provisional 

 in character. Some criticism was directed by Prof. 

 J. C. McLennan at Sommerfeld's extension of Bohr's 

 theorv in connection with the fine structure of spec- 

 tral lines. Prof. McLennan 's experiments with the 

 lines in the Balmer series of hydrogen did not indi- 

 cate quantitative confirmation, such as had been 

 claimed in the case of Paschen's work with helium. 

 Dr. Irving Langmuir urged that the mechanism of 

 the quantum theory should be sought for in the elec- 

 tron itself. He believed, for example, that the 

 changes of orbit must be due to discontinuous 

 changes occurring in the structure of the electron, 

 and gave illustrations of what he described as the 

 "Quantum state " of the electron. Mr. C. G. Darwin 

 replied to the discussion. Altogether, although of 

 necessity' somewhat disjointed, it proved of absorbing 

 interest. 



A paper was read by Prof. C. G. Barkla on "The 

 Energy of X-radiation." In this the author explained 

 the distinct properties of scattered X-radiation and 

 fluorescent or characteristic radiation. In the former 

 the laws of classical mechanics applv and all atoms 

 contribute; in characteristic radiation quanta un- 

 doubtedly operate, and only a minute fraction of 

 the at(xns take part, these being in an abnormal 

 state. 



In the Mathematical Sub-Section three papers were 



