June 2, 1921] 



NATURE 



445 



computation of a single trial period under the periodo- 

 gram arithmetical method. — Dr. G. R. Goldsbrough : 

 The influence of satellites upon the form of Saturn's 

 ring. The ring is supposed to be made up of small 

 particles arranged in concentric circles and rotating 

 about the primary. The satellite is assumed to follow 

 an unperturbed circular orbit, and the influence of the 

 rings upon one another is assumed negligible. To a 

 close degree of numerical approximation the satellite 

 Mimas is responsible for the position and width of 

 Cassini's Division and for the clean-cut termination 

 of the whole ring. Satellite Rhea accounts for the 

 clean-cut commencement of the inner ring (or ring B), 

 while a probable explanation is offered of the exist- 

 ence of the crepe ring. If m be the mass of any 

 particle, and M the mass of Saturn, and n the number 

 of particles in any single ring, it is shown that 



0<m/M<i-8/n'. 

 The maximum mass of a particle is thus just below 

 the limit given by Maxwell. — Dr. H. Jeffreys : Certain 

 geological effects of the cooling of the earth. 

 Mechanical consequences of the cooling of the earth 

 from its formation to its present state are considered. 

 The former fluidity of the earth is assumed and the 

 information provided bv radio-activity is utilised. The 

 thermal contraction available for mountain-building 

 is of the same order as that required to account for 

 existing mountains. Ihc Pacific type of mountain 

 range can be explained as due to greater cooling and 

 consequent greater strength of the rocks below the 

 ocean. Isostatic compensation of surface inequalities 

 is due to variation in the thickness of the light rocks 

 constituting the crust, combined with plastic flow 

 below. The fact that oceans have extensive regions 

 of less depth in the middle is explained and theories 

 of the formation of continents and geosvnclines are 

 suggested.— T. Kikuchi : The moving striations in a 

 neon tube. 



Geological Society. May 4.— Mr. R. D. Oldham, 

 president, in the chair. — H. Hamshaw Thomas : An 

 Ottokaria-like plant from South Africa. The dis- 

 covery in the Vereenijring- Sandstones of the Transvaal 

 of a fossil plant which bears considerable resemblance 

 to the genus Ottokaria is recorded. The specimen 

 agrees with known examples in size, and in having 

 an almost circular head seated upon a stalk ; an addi- 

 tional feature is a thin flattened structure projecting 

 beyond the head, provisionally called the "wing." 

 Ottokaria was probably a reproductive structure, and 

 its association with Glossopteris suggests a possible 

 connection with this plant. The name of Ottokaria 

 Lesliei is assigned to the specimen. — Dr. A. B. 

 Walkom : On Nummulosoermum, gen. nov., the prob- 

 able megasporangium of Glossopteris. Seed.s asso- 

 ciated with some fronds of Glossopteris from Queens- 

 land are described under the name Nummulospermum 

 bowenense. The vascular system is also partlv de- 

 scribed. The seeds have not been found in actual con- 

 nection with Glossopteris fronds. Remarks are added 

 on the scale-leaves of Glossopteris, and on the aflfini- 

 t'es of Glossopteris, which is classed with the Cycado- 

 filicales. The anatomical features of the seeds sug- 

 gest relationshio with the Trigonocarpales. — Agnes 

 McDonald and Dr. A. E. Trueman : The evolution of 

 certain Liassic gastropods, with special reference to 

 their use in stratigraphy. The gastrooods dealt with 

 are turriculate forms, formerly called Cerithium, now 

 referred to the family Procerithidae, Cossmann, and 

 Chemnitzia. now referred to the family Loxone- 

 matidae. Koken. Sue"gestions for the classification 

 of these gastropods, based on ontogenetic and other 

 evidence, are made. The position and characters of 

 the ornamentation have proved of value in classifica- 



NO. 2692, VOL. 107] 



tion, when taken in conjunction with the other char- 

 acters of the shell. In numerous series acceleration 

 or retardation of development is indicated, and 

 examples of homoeomorphy of several types have been 

 noted. The Procerithidae of the Lower Lias are 

 chiefly species of Procerithium, in which the flattish 

 whorls have reticulate ornament based on three 

 spirals. This series probably gave rise to many recent 

 Cerithidae which have more than four spirals. Other 

 genera of Procerithidae are recognised. The pupoid 

 forms which have been grouped in the genus Exelissa 

 are regarded as catagenetic descendants of diverse 

 species of Procerithium. The Loxonematidae of the 

 British Lias are of two types, one with axial orna- 

 ment (Zygopleura), the other with axials and feeble 

 spirals (Katosira). Each of these genera shows 

 during the Lias an increase in the number and curve 

 of the axials. In development axials always appear 

 before spirals among the Loxonematidae, while spirals 

 are developed first among the Procerithidae. 



Physical Society, May 13. — Sir William Bragg, presi- 

 dent, in the chair.— L. Hartshorn and E. S. Keeping : 

 Notes on vacuum tubes used as detectors of electrical 

 oscillations. The paper describes the development of 

 a robust form of vacuum tube which was used as a 

 detector of electrical oscillations in the "wireless" 

 circuits carried by aeroplanes. Platinum electrodes are 

 avoided, being replaced by strips of tinfoil, to which con- 

 tact may be made by the spring clips holding the tube 

 in position. It was found that when a discharge is 

 passed through such a tube the walls are affected in 

 such a way that thenceforth it is much easier to get 

 a discharge to pass. The change produced by the first 

 discharge is annulled by heating the tube above 210° C. 

 Further, if the walls are coated on the inside with a 

 metallic film, this first discharge is unnecessary, and 

 the tube is unaffected by heating, but when the walls 

 are coated with an insulator it ;s, if anything, more 

 difficult to pass a discharge. A silica tube behaves like 

 one coated with metal. It seems possible that the 

 change in the tube may be due to the formation of a 

 layer of gas molecules on the walls bv the first dis- 

 charge. The explanation of the behaviour of the silica 

 tube is a difficulty.— B. W. Clack : The coefficient of 

 diffusion of certain saturated solutions. This paper 

 gives an account of experiments on the diffusivity of 

 saturated solutions of KCl, NaCl, and KNO3 at con- 

 stant temperatures near 18° C, when the steady 

 state of diffusion has been attained, employing a 

 method similar to that previously used by the author 

 (Proc. Phys. Soc., vol. xxi., p. 863, 1908; vol. xxiv., 

 p. 40, 1911; vol. xxvii., p. 56, 1914; vol. xxix., p. 49, 

 1916). The solution under investigation is maintained 

 at complete saturation by the presence of salt crystals 

 in the diffusion vessel ; the theory takes into account 

 the change in volume of this salt as it dissolves, and 

 an expression is obtained for the coefficient of diffusion 

 at complete saturation, which depends on the rate of 

 change in weight of the diffusion vessel with time. 

 The experimental results are found to agree very 

 closely with the values obtained by extrapolation from 

 the results previously found for less concentrated solu- 

 tions. By the present paper the author has thus ex- 

 tended the range of concentration over which he has 

 studied diffusion from very dilute solutions right up 

 to complete saturation. — Dr. G. D. West : Experi- 

 ments on thermal transpiration currents. Theoretical 

 considerations are first introduced to show that if a 

 radial temperature gradient be maintained over a disc 

 so that the centre is the hottest part, thermal transpira- 

 tion currents sweep radially inwards over the surface 

 of the disc, and discharge themselves more or less 

 radially outwards in the upper regions. To detect 



