38 



NATURE 



[March 13, 1919 



rotatory property. Owing to rotatory dispersion the 

 period is different for different wave-lengths, and 

 coloured bands result. The clearest and whitest 

 quartz has some scattering power, though much less 

 than that of glass or liquids. In one case examined 

 the intensity was about eight times that due to dust- 

 free air at atmospheric pressure. This small scatter- 

 ing is considered to be due to inclusions, as in the 

 case of visibly smoky or yellow quartz. The regular 

 atomic structure, which has a period small com- 

 pared with the wave-length of ordinary light, should 

 give no scattering. For very short wave-lengths 

 (X-rays) the well-known diffraction effects of crystals 

 come in. — Sir James Dobbie and Dr. J. J. Fox: The 

 constitution of sulphur vapour. Investigations based 

 on the determination of the vapour density leave the 

 question of the existence of sulphur molecules inter- 

 mediate in complexity between S, and S^ unsettled. 

 The present paper contains an account of an attempt i 

 to solve the problem by the study of the absorptive 

 power of the vapour of sulphur for light under various 

 conditions of temperature. When light from a suit- 

 able source is passed through the vapour and 

 examined with the spectroscope at successively higher 

 temperatures it is found that the amount of absorp- 

 tion caused by the vapour gradually increases up to 

 about 650° C, after which it decreases as the tem- 

 perature rises until 900° C. is reached, above which 

 no further change occurs. — Dr. W. G. Duffield, T. H. 

 Burnham, and A. H. Davis: The pressure upon the 

 poles of the electric arc. For many reasons the pro- 

 jection of electrons from the cathode of an electric 

 arc is to be expected, and the mechanism of the arc 

 appears to require it. If this projection exists, it is 

 likely to occasion a mechanical recoil upon the 

 cathode. A pressure was looked for in 19 12 and dis- 

 covered. It remained to determine if the magnitude 

 was such as to be accounted for by electronic projec- 

 tion. Numerous sets of observations upon anode and 

 cathode were taken with varying current and arc- 

 length and different dispositions of apparatus. The 

 pressure was found to be about 0-17 dyne per ampere, 

 or when convection current effects were eliminated 

 so far as possible, 022 dyne per ampere. The effect 

 does not appear to be due to radiometer action, and 

 is about two hundred times too small to be referred to 

 the expulsion of carbon atoms at the boiling-point 

 of that element. Such evidence as has been obtained 

 thus favours the recoil being due to the projection of 

 electrons. 



' Physical Society, February 14. — Prof. C. H. Lees, 

 president, in the chair.— S. 'Skinner and R. W. Burfitt : 

 Temperature coefficient of tensile strength of water. 

 The liquid is forced under pressure through a capillary 

 constriction between two limbs of a U-tube. By trial 

 the pressure is adjusted until the speed in the capillary 

 is sufficient to produce rupture. This is judged by 

 the sound and also the appearance. The whole U-tube 

 is immersed in a bath, the temperature of which can 

 be varied. Actual observations of rupture, velocity, 

 and temperature are recorded up to about 100° C, 

 from which it is deduced that the tensile strength 

 becomes zero in the neighbourhood of 245° C, which 

 is in agreement with theory. — Prof. W. H. Eccles : 

 Vector diagrams of some oscillatory circuits used 

 with thermionic tubes. The method of the 

 crank or vector diagrams used commonly in 

 the studv of alternating-current circuits is ap- 

 plied in the paper to the assemblage made up of 

 an oscillator, the thermionic relay maintaining it in 

 oscillation, and the devices linking these two parts. 

 The diagrams then serve as substitutes for the usual 

 treatment of the problem by differential equation, and 

 from them may be obtained all the formulae. They 

 NO. 2576, VOL. 103] 



have, besides, the advantage of exhibiting to the eye 

 the phases of the currents and voltages in every part 

 of the circuits. In forming the diagrams the potential 

 drop across the oscillator is calculated by the usual 

 rules of the alternating-current diagram, and added 

 geometrically to the potential drop across the tube. 

 This total is made equal. In magnitude and phase, to 

 the voltage applied at the Instant to the grid multi- 

 plied by the voltage factor of the relay. In its turn 

 the voltage applied to the relay depends upon, and is 

 obtained from, the current running In a portion of the 

 oscillator. The fitting together of these lines gives all 

 the conditions to be satisfied for the maintenance of 

 steady oscillations. — Prof. W. H. Eccles and F. W. 

 Jordan : A small direct-current motor using thermionic 

 tubes instead of sliding contacts. In this motor the 

 rotating part is an ebonite disc with iron teeth on Its 

 periphery, and the stationary part comprises two 

 electromagnets with their poles close to two teeth. 

 One electromagnet is connected to the grid of a 

 thermionic relay, the other is included in the plate 

 circuit. When during rotation a tooth passing the 

 grid magnet Induces a voltage In Its winding, the 

 consequent transient Increase of current through the 

 other magnet causes this magnet to exert a pull on 

 the tooth approaching it. We thus have a small motor 

 without commutator or spark which may under no- 

 load be driven up to a speed of 4000 to 6000 revs, per 

 itiin. from the lighting supply. 



Geological Society February 21. — Mr. G. W. 

 Lamplugh, president, in the chair. ^ — Annual general 

 meeting. — G. W. Lamplugh : Presidential address : 

 The structure of the Weald and analogous tracts, 

 (i) The anticline of the Weald is a superficial structure 

 dependent upon an underlying syncllne. The lens of 

 sediments thus bounded wa§ deposited In a gradually 

 deepening trough, which \vas afterwards shallowed by 

 partial recovery. (2) The Jurassic rocks of the rest 

 •of England have had a similar history, and show an 

 analogous structure modified by unequal uplift. 

 (3) The Triassic and most of the Carboniferous rocks 

 of England appear also to have been accumulated in 

 deepening troughs or basins, which were afterwards 

 shallowed by differential uplift where the deposits 

 were thickest. (4.) Where the formations dealt with 

 lie above sea-level, the present outcrops represent the 

 areas of maximum development, and therefore co- 

 incide roughly with the position of the deepest parts 

 of the old troughs. This factor may be of wide 

 application, and has a practical bearing. 



February 26. — Mr. G. W. Lamplugh, president, in 

 the chalr.^— Col. T. W. Edgeworth David : Geology 

 at the Western Front. 



Zoological Society, March 4. — Dr. k. Smith Wood- 

 ward, vice-president, in the chair.— G. A. Boulenger : 

 Fishes from Lake Tanganyika, Including three new 

 species.— Miss Joan B. Procter : The skull and affinities 

 of Rana. suhsigillata. Attention was directed to several 

 cranial characters either peculiar to this frog or held 

 In common with R. adspersa, its nearest ally. 



Dublin. 



Royal Irish Academy, January 27. — Mr. T. J. 

 Westropp, vice-president, in the chair.— R. LI. Praeger : 

 Species of Sedum collected in China by L. H. Bailey 

 in 1917. The collection included three new species, 

 S. limuloides, S. haileyi, and S. quaternatmn. the first 

 being a remarkable plant of doubtful affinities, and the 

 second a member of a group (Involucrata) confined 

 as hitherto known to the Caucasus and -Asia Minor. 



Februarv 10.— Prof. G. H. Carpenter, vice-president, 

 in the chair.— A. Henry and Miss M. G. Flood : The 

 historv of the London plane, Plaianus acerifolia. 

 This tree unknown In the wild state, and invariably 



