398 



NATURE 



[July 17, 19 1< 



and must sign an agreement, with the concurrence of 

 his parents or guardians if a minor, to enter the office 

 of a surveyor approved by the council with the view 

 of practising as a surveyor in the future, or as an 

 alternative to engage in advanced research work in 

 subjects approved by the council as of value to the 

 profession, and in due course to sit for the inter- 

 mediate and final examinations of the institution. 

 Election to the scholarships will be by competitive 

 examination conducted by the Oxford and Cambridge 

 Joint Examination Board. In the examination candi- 

 dates will be required to write an English essay 

 chosen from four subjects set by the examiners and to 

 present themselves for examination in either (a) lan- 

 guage, (b) mathematics, or {c) science. If (a), not 

 more than two of the following : Latin, Greek, 

 French, German ; if (b), mathematics only, or mathe- 

 matics and one science subject; if (c), not more than 

 two of the following : physics, chemistry, botany, 

 physical geography, and elementary geology. The 

 next examination will bei held about the end of 

 January. Entries should be addressed to the Secoe- 

 tary of the Surveyors' Institution, 12 Great George 

 Street, Westminster, by December 15 next. 



SOCIETIES AND ACADEMIES. 

 London. 

 Royal Society, June 26.— Sir J. J. Thomson, presi- 

 dent, in the chair.— Dr. A. E. H. Tutton : Monoclinic 

 double selenates of the cobalt group. This memoir 

 deals with the four double selenates of the series 

 R,M(SeO,)2-6H20, in which M is cobalt and R is 

 potassium, rubidium, caesium, and ammonium. A 

 complete crystallographic and physical investigation 

 has been carried out on parallel lines to the work 

 previously published concerning the magnesium, zinc, 

 iron, and nickel groups, and to that concerning the 

 complete analogous series of double sulphates. The 

 results are in full accord with those derived from the 

 previous investigations. Two dominant facts emerge, 

 namely, (i) the progressive order of all the crystallo- 

 graphic and physical properties, following the progres- 

 sion of the atomic numbers (and therefore atomic 

 weights) of the interchangeable alkali metals con- 

 cerned, potassium, rubidium, and caesium ; and 

 (2) the almost perfect isostructure— that is, con- 

 gruency, coincidence, and equality of dimensions of 

 the elementary cells of the monoclinic space-lattices— 

 of the crystals of the ammonium and rubidium salts 

 of the group. The progression with atomic number 

 referred to under (i) is completely explained by the 

 operation of Moseley's law, governing the progres- 

 sive structural complexity of the atoms in accordance 

 with the sequence of the atomic number. — Hertha 

 Ayrton : A new method of driving off poisonous gases. 

 — Dr. F. W. Aston : Experiments with perforated 

 electrodes on the nature of the discharge in gases at 

 low pressure. Ex,periments are described on the dis- 

 charge between electrodes of a large flat form per- 

 forated with a long narrow slit, the charge passing 

 through the slit being collected and measured in a 

 Faraday cylinder. Direct measurements made with 

 the Faraday cylinder behind the cathode and at the 

 same potential seem to indicate that about half the 

 total current in the discharge is brought up to the 

 cathode by positive ions. Attempts to discover the 

 distribution of velocities in this stream show that this 

 is not directly determinable, owing to the very high 

 ionisation in the region of the slit and other reasons, 

 which are discussed. Using a perforated anode, it is 

 found that as the distance from the cathode is in- 

 creased arithmetically the current carried by the 

 cathode rays into the Faraday cylinder decreases geo- 



NO. 2594, VOL. 103] 



metrically when the current is constant.— Mary Seegar 

 and Prof. Karl Pearson : De Saint- Venant solution for 

 the flexure of cantilevers of cross-section in the form 

 of complete and curtate circular sectors; and the 

 mfluence of the manner of fixing the built-in end of 

 the cantilever on its deflection.— Dr. H. Jeffreys : The 

 relation between wind and the distribution of pres- 

 sure. _A classification of some six hundred wind ob- 

 servations over the North Sea, according to their 

 velocities and directions, showed that the most strik- 

 ing feature of the resulting values was their asym- 

 metrical frequency distribution. From the fact that 

 this was noticeable in nearly every class, it was 

 inferred that it could be produced only by variation in 

 turbulence or systematic contortion of the isobars, on 

 a scale too small to be recorded on the weather map. 

 The latter cause, however, and also such variations in 

 turbulence as keep the coeflficient of eddy viscosity the 

 same at all heights, would lead to strong correlations 

 between S/G and a, which are not observed. Hence 

 it is concluded that the principal cause of variation 

 in the relation of the surface wind to the gradient is 

 variation in the vertical distribution of turbulence ; and 

 it is shown that such variation could give the effects 

 actually observed.— Prof. C. H. O'Donoghue : The 

 blood vascular system of the Tuatara, Sphenodon 

 punctatus.—G. H. Livens : The fundamental formula- 

 tions of electro-dynamics. The object aimed at in this 

 paper is the removal of certain difficulties and dis- 

 crepancies which exist in the usual formulations of 

 electro-dynamic theory. After a brief statement of 

 the differential theory in which a new equation, 



is introduced to express the time-rate of change of 

 the magnetic force H when the magnetic media are in 

 motion with a velocity v, a general formulation of 

 the theory based on the principle of least action is 

 developed, in a manner which leads directly to ex- 

 pressions for the intrinsic energies of the polarised 

 media, for the forces per unit volume on the polarised 

 and charged media, and, finally, for the complete 

 electro-motive force on the moving electrical elements. 

 —Dr. A. E. Oxley : The influence of molecular con- 

 stitution and temperature on magnetic susceptibility. 

 Part iv. : Further applications of the molecular field. 

 The main paper is a continuation of the work pub- 

 lished in Royal Society Transactions, A, vols, ccxiv. 

 (1914), and A, ccxv. (1915), and Royal Society Pro- 

 ceedings, A. vol. xcv. (1918). It deals with the addi- 

 tional applications of the local molecular forcive in 

 crystalline and vitreous media. It is shown that the 

 change of volume on crystallisation can be interpreted 

 as a magneto-striction effect of the molecular field. 

 The molecular field is assumed to be proportional to 

 the local intensity of magnetisation, the coefficient of 

 proportionality being the reciprocal of the limiting 

 susceptibility under field strengths equal to the respec- 

 tive molecular fields at different temperatures. A 

 discussion of the nature of the molecular field is given, 

 and the conclusion is reached that the forces of 

 crystallisation are of a magnetic nature. The large 

 value of the local magnetic forcive suggests that they 

 mav play an important part in chemical combination, 

 and further evidence is given for the existence of the 

 magneton in diamagnetic media. ^ — A. Mallocli : Dif- 

 fusion of light by rain, cloud, or fog. In this note 

 attention is directed to the s.imilarity between the 

 diffusion of light by small drops and the diffusion of 

 heat bv conduction. The drops under consideration 

 are supposed to have, at least, diameters of many 

 wave-lengths of the light scattered by them, so that 

 peculiarities of diffusion dependent on the relation of 



