June i8, 1908] 



NA TURE 



167 



Edinburgh. 

 Royal Society, May 4. — Prof. Crum Brown, vice- 

 president, in the chair. — Sunset and twiliglit curves and 

 related phenomena : D. M. Y. Sommerville. The objects 

 of the paper were (i) to describe certain curves which 

 approximate to tlie graphs of the time of sunset (or sun- 

 rise) and end of twilight (or daybreak) all the year round 

 for various latitudes ; (2) to tabulate the yearly pheno- 

 mena of light and darkness for different latitudes under 

 various conditions. The case of the earth was first dis- 

 cussed, and then the investigation was extended to cases 

 in which the inclination to the ecliptic was given arbitrary 

 values ranging from 0° to 90°, and in which also the same 

 range was given to the limiting depression below the 

 horizon of the sun's centre consistent with twilight con- 

 ditions. The various possible combinations of daylight, 

 twilight, and true night which make up any complete day 

 were examined, and some interesting mathematical rela- 

 tionships obtained. — The electromotive force of iodine con- 

 centration cells in alcohol and water : Principal A. B. 

 Laurie. The results show that if tlie E.M.F. is calcu- 

 lated from the mass equation constant determined by 

 Jakowkin and the Nernst equation for osmotic pressure 

 and E.M.F., the experimental results agree very closely 

 where the potassium iodide is present in excess, but only 

 approximately where the potassium iodide and iodine are 

 present in sensibly the same proportions. In alcohol cells 

 the E.M.F. results show a very close agreement with the 

 Nernst equation for cells in which the potassium iodide is 

 in excess, and also show that there is evidently a similar 

 complex formed in the presence of alcohol as there is in 

 the presence of water. The E.M.F. of cells in which 

 mixtures of alcohol and water are used indicates that at 

 0° C. the dissociation of the potassium iodide is less for 

 such mixtures than it is for alcohol or water, this effect 

 disappearing at 25° C. Experiments with cells in which 

 solutions of equal strength of iodine and potassium iodide 

 ■were used, dissolved in water round the one electrode and 

 dissolved in alcohol round the other electrode, show an 

 E.M.F. of nearly two-tenths of a volt, the water solution 

 being positive, and the action of the cell transferring 

 iodine from water to alcohol and potassium iodide from 

 alcohol to water. This alcohol-water cell has a consider- 

 able temperature coefficient, showing that heat is being 

 absorbed during the passage of the current, but not so 

 large as would be required by the Nernst equation if it 

 was a purely gas-pressure cell. When connected to a 

 galvanometer this cell gives a current for some hours. — 

 Preliminary statement on the morphology of the cone of 

 Lycopodiiim cernuttm and its bearing on the affinities of 

 Spencerites : Dr. \V. H. Lang;. The cone of Lycopodiiim 

 ceniutim is the most complex in the genus, but it was 

 shown that in Spencerites certain of the most character- 

 istic features were either distinctly visible or at any rate 

 strongly suggested. Whatever view of their relationship 

 je taken, there appeared to be a prima facie case for 

 regarding the morphology of the cone as essentiallv thr- 

 same in the two forms. — The origin of the adaxiallv 

 curved leaf trace in the Filicales : D. T. Gwynne Vaughan 

 and Dr. R. Kidston. As exhibited in Thamnoplcris 

 Schlcchtcndali, the le.if traces leave the stele in a 

 thoroughly protostelic manner when free, at first appearing 

 as an oval mass of xylem with a central protoxvlem. 

 While in this form an island of parenchyma appears 

 adaxiallv to the protoxylem, which, gradually increasing, 

 eventually displaces the centripetal xylem. By progressive 

 stages the characteristic leaf trace becomes curved, and 

 assumes the characteristic horse-shoe form so common to 

 the Filicales. — A new species of Dineuron and of Botryo- 

 pteris from Pettycur, Fife : Dr. R. Kidston. — The iiica 

 or inter-parietal bone, its homologv and nomenclature : 

 Dr. W. R. Smith. 



May I.'^. — Prof. A. Gray, vice-president, in the chair. — 

 The cohesion of steel, and. on the relation between the 

 yield points in tension and in compression : G. H. 

 Gulliver. In a homogeneous isotropic solid the directions 

 of maximum shearing stress are inclined at 4^° to the 

 directions of principal stress. Because of internal friction, 

 the surfaces of sliding w'ill be inclined to the direction of 

 maximum tension at an angle which is greater than 45° 

 ty half the angle of friction. Experiments on steel bars 



NO. 2016, VOL. 78] 



lead to the value 0176 for the coefficient of friction, a 

 value which corresponds closely with the ordinary co- 

 efficient of friction for dry metallic surfaces. The shear- 

 ing stress along a surface of sliding is always greater 

 than the frictional resistance due to normal stress upon 

 the same surface. .Assuming this to be due to a cohesive 

 force acting normally to the same surface, the author 

 calculated the value of this cohesion for steel as being 3-384 

 times that which corresponds w-ith the tension yield point, 

 or 2-384 times that which corresponds with the pressure 

 yield point. Experiment fully corroborated this conclusion. 

 Experiments also confirmed the further conclusion that 

 the fracture of a bar under tension begins in a direction 

 normal to the axis. — The preparation of a glass to conduct 

 electricity : C. E. S. Phillips. A mixture consisting of 

 thirty-two parts of sodium silicate, eight parts of borax, 

 and one part of Powell's glass is fused in a platinum 

 crucible. The air bubbles are rapidly removed from the 

 mass by means of a vacuum pump, and the resulting glass 

 pressed into plates or cast in the usual way. The con- 

 ductivity of this material is comparatively high, being 

 about 1000 times greater at 20° C. than ordinary soda 

 glass at 100° C. Its specific resistance is 5x10' ohms at 

 20° C. The index of refraction is 1-6, the density 2-6, 

 and the softening point 551° C. On account of the high 

 coefficient of expansion, viz. 0-00015, the conducting glass 

 cannot be welded to ordinary tubing except by me;ms of 

 glasses with intermediate coefficients of expansion. The 

 study of the surface changes was made by means of an 

 electrical method depending upon the negative electrifica- 

 tion of cadmium when in contact with a moist surface of 

 the conducting glass. It was found in this way that the 

 substance attracted less moisture with time, and therefore 

 slowly improved. Some experiments were shown which 

 proved that the glass conducts electricity through its mass, 

 and that the effect is not merely a surface one. 



Paris. 

 Academy of Sciences, June 9. — M. H. Becquerel in the 

 chair. — An apparatus designed for micrometric levellings : 

 M. Gouy. A microscope furnished with a w'ire micro- 

 meter, and standing upon a tripod the feet of which are 

 ivory points, slides on a plane horizontal disc of polished 

 glass. The micrometer wire being first set on the object 

 the position of which is to be measured, its position on 

 the standard scale is found by sliding the tripod over the 

 disc until the divisions of the scale are in focus. .\s show- 

 ing the accuracy obtainable by this simple method, the 

 probable error of a setting of the micrometer, the micro- 

 scope remaining fixed, Avas found to be 0-043 M. whilst 

 when the microscope was moved over the disc between 

 each setting the probable error of a setting was 0-042 /i. — 

 The direct addition of hydrogen to the polyphenols : Paul 

 E-abatier and .\. Mailhe. Previous attempts to apply the 

 Sabatier and .Senderens reaction to the diphenols and 

 triphenols have failed, due, as is now found, to the employ- 

 ment of too high a temperature in the reaction. -At a 

 temperature of about 130° C, in a rapid current of 

 hydrogen, hydroquinol, pyrocatechol, resorcinol, and pyro- 

 gallol give good yields of the corresponding rycZohexadiols 

 and triols respectively. Hydroquinol gave the ri'i-quinite 

 exclusively, and pyrocatechol and resorcinol also appeared 

 to give the cii-compounds, aithough this point has not 

 yet been completely proved. Since this method yields these 

 compounds easily, and in a very pure state, a special study 

 is being made of the properties of these derivatives. — 

 Magnetic observations at Tananarive : E. E. Colin, Three 

 tables are given showing the results of the absolute 

 measures of declination, of inclination, and of the hori- 

 zontal intensity, from May, 11107, to .April. iqoS. — The 

 exact analysis of marsh gas. The dissociation of several 

 hydrocarbons obtained in the grisoumeter and eudiometer : 

 Nestor Grehant. — The regulation of electrogenic groups : 

 J. L. Routin. — The development in a continued fraction 

 of an algebraical number : M. Auric. — The true cause of 

 the doubling of the curve of loss of activity of conductors 

 covered W'ith a dielectric layer, rendered radio-active, and 

 w-ith an electric charge : Ed. Sarasin and Th. 

 Tommasina. — The sign of electric dichroism and of 

 magnetic dichroism : Georges Meslin. — The self-induction 

 spark : Andre Leaute. The essential cause of the striffi 



