December 2, 1920] 



NATURE 



451 



Under the comprehensive title of " Sterilisation of 

 Water by Chlorine Gas" a paper by Capt. J. Stanley 

 Arthur was read before the Institution of Mechanical 

 Engineers on November 19. The part of the paper 

 dealing with the general aspect of the subject adds 

 little or nothing to our knowledge, and contains 

 statements which, to say the least, are still debatable. 

 For example, the author states that water treated 

 with chlorine gas is less liable to an objectionable 

 taste than when treated with bleaching-powder, and, 

 further, that any taste so imparted can readily be 

 removed by the addition of sulphur dioxide. Other 

 experimenters have found that there is little or no 

 difference between bleaching-powder and chlorine gas 

 as regards taste, and also that some tastes produced 

 by chlorination are absolutely unaffected by the further 

 addition of sulphur dioxide. Also, no mention is 

 made of the pioneer work on chlorination of Houston 

 and McGowan at Lincoln in 1905 or of any of 

 Houston's later work on the subject. The greatdr 

 part of the paper consists of the detailed description 

 of an .American device for accurately administering 

 the dose of chlorine and its adaptation for the purpose 

 of sterilising the water-supply to the troops during the 

 war. These descriptions are very clearly stated and 

 well illustrated with careful drawings. No other 

 types of chlorinators are described, although there are 



others equally efficient now on the market. The paper 

 concludes with a warm tribute to Sir William Hor- 

 rocks for his work on water purification for the Army, 

 and is further evidence of the great part played by the 

 sanitary section of the R..A.M.C. in winning thd war; 

 it is probable, however, that Sir William and his col- 

 leagues would be the first to acknowledge their in- 

 debtedness to others not mentioned in Capt. Arthur's 

 paper. 



The latest catalogue (No. 407) of second-hand books 

 offered for sale by Mr. F. Edwards, 83 High Street, 

 Marylebone, W.i, is devoted to botany, ranging over 

 the subjects of agriculture, gardens, orchids, trees, 

 fruits, fungi, lilies, and roses. It should be of interest 

 to many readers of Nature. Many choice and rare 

 works are listed, among them several herbals, a com- 

 plete set of the Annals of Botany, Curtis' Botanical 

 Magazitie, 1787-1915, and Sir J. D. Hooker's "Botany 

 of the Antarctic," 6 vols. 



We are informed that the office of the Assistant 

 Commissioner of Forestry for England and Wales 

 (Mr. Hugh Murray) is now situated at 30 Bclgrave 

 Square, London, S.W. i. The headquarters of the 

 Commissio/i remains at 22 Grosvenor Gardens, 

 London, S.W. i. 



Our Astronomical Column. 



I HE Leo.vid Meteoric Shower. — Mr. Denning 



ites that on November 15 and 16 the Leonids re- 



' :ied in moderate numbers. Mr. C. P. Adamson, 



-•-■rving at Wimborne, Dorset, watched the sky 



ring a period of ten hours, and saw thirty-three 



nids out of a total of ninety-eight meteors re- 



' Ic-d. The radiant point was placed at i5o°+22°, 



the display furnished objects of the usual swift 



' streak-leaving character. 



Miss A. Grace Cook, at Stowmarket, also witnessed 



the return of the meteors on the same nights and 



determined the radiant in precisely the same position 



Mr. .\damson. Mr. A. King made observations 



n Lincolnshire, and on November 15, during a 



■(.h of three hours between iih. i8m. and 



. 37m., saw thirty meteors, of which nine were 



i.-onids directed from a radiant at 152°+ 23°. Other 



showers were seen from 63°+ 22° (five meteors), 



"'7° + 3.'>' (seven meteors), and ii6°+49'' (fi^c 



leors) at the middle of November. 



The reappearance of the Leonids adds another link 



<hf chain of past observations, which prove that 



stream of meteors is visibly continuous through- 



the entire orbit, and that it may be viewed cvcrv 



1-November when the prevailing atmospheric rondi- 



lis arc favourable. 



K\PI\TION PrF.SSI-RE OS Er.ECTRONS AM) .\lO.MS. — 



Mr, Lr-igh Page discusses this subject in Astrophys. 



TM for September. It was formerly concluded that 



Ti pressure reached a maximum for particles 



winters comparable with a wave-length, and 



('■ii off rnpidiv for smaller particles. The present 



^por shows that this result neglects resonance, and 



fhat the radiation pressure on an atom "depends on 



he intensity of that portion of the incident radiation 



l^hich has n frequcnrv equal to the natural frequency 



it the oscillator." It Is deduced that the pressure 



|>f solar radiation is greatest on an atom which has n 



pson.-int frequency in the infra-red near to wave- 



length 9000 A., being within one-third of this maxi- 

 mum value for the range 4000 A. to 28,000 A. The 

 pressure may be further increased if the atom has 

 more than one resonant frequency. 



It is shown that in certain circumstances the 

 repulsive force may be thirty times that due to 

 gravitation. It thus seems sutticient to explain most 

 of the phenomena of comets' tails, and removes the 

 difficulty formerly felt, namely, that the spectroscope 

 shows the presence of certain gases in the tail, for 

 the molecules of which the pressure was thought to 

 be negligible. The author states that since writing 

 the paper he has found that some of his conclusions 

 were published bv M. Gouy in 1913 (Comptes rendus, 

 vol. civii., p. 186). 



Pkrtl'rbations in a Stellar Orbit.— There arc not 

 many cases where perturbations in stellar orbits can 

 be observed with any degree of accuracy. Mr. J. S. 

 Paraskevopoulos examines the case of 13 Ceti in 

 Astrophys, Journ. for September. This is a visual 

 binary with a period of 688 years, while the brighter 

 star is a spectroscopic binary with a period of 20818 

 days. The eccentricity of the orbit of the visual pair 

 is 0-725. The author has rcmeasured a number of 

 spectrograms taken at the Ycrkes Observatory 

 bietween 1906 and 1913, deducing separate orbits at 

 three different epochs. These show that tlie period 

 is shorter by 1/200 day at apastron of the visual 

 companion than at poriastron, this being analogous 

 to the period of the moon at aphelion and perilK-lion. 

 Motion of the line of apsides is well established. It 

 is concluded that the mass of the visual companion 

 docs not fall far short of, and may exceed, that of 

 the spectroscopic pair. Taking the parallax as 

 o-o^o' (J. A. Miller), m/M becomes i-m. 



"the system 85 Pegasi is referred to, in which Prof. 

 O. Van niesbrocck deduced that the mass of the 

 brighter componrni was only 0-36 of that of the 

 whole system. 



NO. 2666, VOL. 106] 



