November 5, 190S] 



NA TURE 



23 



The proceedings of the general physics department 

 began with a paper from Sir W. Ramsay with the title 

 " Uo the Radio-active Gases (Emanations) belong to the 

 Argon Series? " The experimental part consisted in the 

 examination of the residues of the fractionation of 120 

 tons of liquid air with the object of discovering new 

 elements. The final residue of 03 c.c. had a spectrum 

 differing in no respect from xenon, and it is concluded 

 that if there is a heavier constituent in air than xenon 

 its amount does not exceed 1/25 billionth of the whole. 

 A consideration of the periodic table reveals gaps at 178, 

 216, and 260, and it is rendered probable that they are 

 respectively unstable emanations, viz. those of thorium, 

 radium, and actinium. Discussing this paper, Prof. 

 Rutherford outlined his well-known argument from the 

 mode of disintegration of uranium and its successors that 

 radium emanation has an atomic weight of 222, but did 

 not attribute importance to the difference between this 

 and 216. It is not possible to apply the same argument 

 to the other radio-active elements, because more than one 

 alpha particle may be thrown off at a time. Actinium, 

 he thought, might belong to a side branch. It seemed 

 improbable that there should be an emanation higher than 

 uranium, and therefore he discountenanced the view that 

 the value 260 belonged to actinium emanation. Mr. S. 

 Russ observed that he recently made a direct comparison 

 between the coefficients of diffusion of the emanations from 

 thorium and actinium, with the result that the molecular 

 weight of that of actinium is less than that of thorium. 

 Sir W. Ramsay, in replying, urged that Prof. Rutherford 

 had left out of account the production of neon, which 

 must be explained by the occurrence of a group of alpha 

 particles. Prof. Rutherford rejoined that he was not con- 

 vinced of the production of neon in radio-active changes. 



Mr. W. Makower followed with a paper on the number 

 and absorption of the 3 particles emitted by radium. The 

 law of absorption by glass found for the & rays from 

 radium B and C is the same as that for aluminium found 

 by H. W. Schmidt, the radiation being measured in both 

 cases by the ionisation produced by the rays after 

 traversing different thicknesses of glass. It was found to 

 be the same when measured by the charge received by an 

 insulated brass cylinder (which surrounded the glass tube 

 containing the emanation), different thicknesses of glass 

 being interposed. It is concluded that when rays pass 

 through matter the absorption is not due to scattering, 

 but to an actual stoppage of the particles. The number 

 of ;8 particles emitted per second by the radium C in 

 equilibrium with i gram of radium is found experiment- 

 ally to be 4-gxio'°. Prof. Rutherford explained that the 

 value he expected from theoretical considerations for the 

 number from both B and C was 6-8xio'° instead of 

 9-8x10'° as deduced from Mr. Makower's experiments. 

 To remove the discrepancy we might assume not merely 

 one o for one $ particle. Prof. McClelland welcomed the 

 view that scattering is not an important factor, though 

 his recent experiments show that some scattering is pre- 

 sent, together with a sending out of secondary particles. 

 Prof. J. J. Thomson had not the slightest doubt, from his 

 own experiments, that there is a large amount of scatter- 

 ing, and that absorption is due to this divergence. The 

 ultimate fate of a particle may be that it sticks in, but it 

 is repeatedly deflected first. Prof. H. A. Wilson expressed 

 an interest in the subject, partly on account of its bear- 

 ing upon his suggestion of the smallness of the o 

 particle. Sir O. Lodge tried to reconcile the opposing 

 statements by asking w-hether it is not necessary to dis- 

 tinguish between absorption by conductors (as in Prof. J. J. 

 Thomson's experiments) and by non-conductors (as in 

 Mr. Makower's). 



.An account was next given by Sir J. Dewar of his 

 recent work on the late of production of helium from 

 radium (v. Proc. Roy. Snc, A, vol. Ixxxi., No. 547, p. 280). 

 After extreme precautions, the rate of production is found to 

 be about 0-37 cubic mm. per gram per dav, a number which 

 is of the same order of magnitude as Rutherford's theory 

 requires. Turning to the question of the helium in the 

 atmosphere, he considered that two or three million vears 

 would be required to produce it from rocks. Prof. R. J. 

 Strutt remarked that 100 billion tons of rock would be 

 required if the supply of helium were kept up in this way. 



NO. 2036, VOL. 70] 



Probably the supply is supplemented by a store in the 

 interior of the earth. A difficulty in making a trustworthy 

 estimate of geological time arises from the fact that helium 

 escapes. Sir O. Lodge pointed out that the rock required 

 would only occupy 20 kilometres cube — a very moderate 

 amount. 



In the department of cosmical physics. Prof. J. Milne, 

 in introducing the report on seismological investigations, 

 remarked on the necessity for accurate time signals in 

 seismological work and the difficulty of arranging terms 

 with the Post Office for the transmission of such signals 

 to the central observatory at Shide. After a short ex- 

 planation of the instrumental records obtained and a state- 

 ment of the shocks noted in 1907, he proceeded to point 

 out that earthquakes travelled more freely towards the 

 west, or against the motion of the earth, than towards 

 the east, while very few earthquakes travelled across the 

 equator. A very important section of this year's report 

 is a catalogue of nearly goo earthquakes recorded in China 

 between 1800 B.C. and 1834 a.d. 



The remaining papers were astronomical in character. 

 Sir Robert Ball described a generalised instrument pre- 

 senting the features common to the altazimuth, meridian 

 circle, prime vertical instrument, equatorial, and almu- 

 cantar, and a single set of equations represented the 

 coordinates of the star relatively to three rectangular axes 

 which could be defined in the generalised instrument. 



Sir Howard Grubb described a new form of divided 

 object-glass telescope in which the two half object-glasses 

 are reversed and placed back to back ; this arrangement 

 permits the use of the necessary diaphragms, and a 

 circular wedge is conveniently employed over one half for 

 producing a relative shift of the rays through the two 

 halves. Sir Howard Grubb also read a paper on the re- 

 flecting telescope and its suitability for physical research — 

 an historical account of the subject. In the discussion 

 Prof. H. H. Turner emphasised the importance of 

 Common's work in connection with the reflecting telescope, 

 and Sir D. Gill advocated the use of the Cassegrain form 

 modified by Hale. Father Cortie described a reflector he 

 had used at .Stonyhurst for solar work, and mentioned 

 the advantage of speculum metal over silvered glass for 

 violet and ultra-violet light. 



Sir Howard Grubb gave a description of the new spectro- 

 holiograph for the Madrid Observatory, which, instead of 

 sliding in a straight line as usual, describes the arc of a 

 circle of which the object-glass for focussing the sun's 

 image is the centre. 



.V paper was next read by Prof. H. H. Turner on the 

 relation between intensity of light, time of exposure, and 

 photographic action. Representing these by the letters I, 

 t, and E respectively, a new law, EccK"'', is given as 

 closely representing the facts concerning stellar photo- 

 graphic effect instead of the law Eo:I(. This means that 

 with an increase of exposure equivalent on the old scale 

 to five magnitudes only four were obtained. Sir W. 

 .\bney stated that since the sensitiveness of a plate is 

 different for different wave-lengths, the full equation must 

 contain a term involving \. Mr. R. T. A. Innes sug- 

 gested the possibility of an influence arising from the 

 diameter of the stellar image. Sir D. Gill felt that the 

 law should be accepted with reservation, since different 

 observers obtained different results, but Prof. Turner, in 

 replying, contended that all observers got the same results 

 if they only knew it. 



Prof. F. W. Dyson contributed a paper on the 

 systematic motion of the stars, which gives the results 

 obtained so far from an unfinished investigation. It 

 appears that the stars of large proper motion (>2o'' per 

 century) have apparent drifts to two points in the sky, 

 but a dirficulty is presented in the explanation of this 

 as due to two streams. Mr. A. S. Eddington thought 

 that the inequality in the numbers of stars in the two 

 streams could be explained by the omission of stars of 

 small proper motion, but admitted that his own results 

 niicht ultimately require modification. 



The proceedings on Monday, September 7, began in 

 general session with a discussion on the theory of wave 

 motion. This was opened by Prof. Horace Lamb, who 

 explained that his object was to establish a better under- 

 standing between students of mechanics and meteor- 



