482 



NA TURE 



[March 14, 1901 



fade almost away, others become stronger. The changes are 

 more marked in the arc spectrum and still more in the spark 

 spectrum of iron. 



A new line of potassium with variable intensity. This line, 

 wave-length approximately 4642, varies in intensity within some- 

 what wide limits. In a given flame its brilliancy is increased by 

 diminishing the quantity of metallic vapour in the flame : this 

 does not appear to depend altogether on the weakening of the 

 continuous spectrum ; it is probably due, in part at least, to the 

 increased freedom of motion permitted to the molecules of the 

 metal. 



Feb'uary 21. — "Notes on the Spark Spectrum of Silicon 

 as rendered by Silicates." By W. N. Hartley, F.R.S. 



March 7. — "On the Composition and Variations of the 

 Pelvic Plexus in Acanthias viilgari<!.'" liy Mr. R. C. Punnett, 

 B.A., Gonville and Caius College, Cambridge. Communicated 

 by Dr. H. Gadow, F.R.S. 



" Preliminary Communication on the Qllstrous Cycle and the 

 Formation of the Corpus Luteum in ihe Sheep." By F. H. A^ 

 Marshall, B A. Communicated by Prof. J. C. Ewart, F.R.S. 



Physical Society, March 8. — Dr. R. T. Glazebrook, 

 foreign secretary, in the chair. — A paper on a theory of colloidal 

 solutions was read by Dr. F. G. Donnan. Assuming that a 

 colloidal solution is not a true molecular intermixture, but a two- 

 phase system consisting of exceedingly minute aggregates of the 

 colloid distributed throughout the solvent, the object of the 

 paper was to examine how such a state of affairs might be 

 imagined to come about. By applying the fundamental notions 

 of Laplace's theory of capillary forces to the statical (mechanical) 

 equilibrium at the interface, it was shown that under certain 

 conditions matter in bulk might disintegrate into a homogeneous 

 liquid medium and yet not attain a state of molecular division, 

 remaining distributed in the form of very thin filaments or sheets 

 whose thickness is comparable with the sphere of molecular 

 attraction. True solution, or molecular intermixture, is re- 

 garded, on the other hand, as arising from the kinetic flux of 

 molecules across the interface. Dr. Gladstone said that the 

 study of colloids was one which had been too much neglected. 

 It involves both a knowledge of physics and of chemistry. A 

 colloid is an unstable bady and is always altering its composition. 

 Water of combination is given off on heating, even if the sur- 

 rounding atmosphere is saturated, and the colloid cannot take 

 up the water again. It is impossible to separate colloids and 

 crystalloids — they merge into one another. The transition 

 forms are not uncommon. Dr. Lehfeldt asked if it had been 

 proved that colloids have osmotic pressure. Prof. Threlfall said 

 that in colloidal solutions some of the substance was not in 

 suspension. Dr. Martin had filled a filter with silicic acid under 

 pressure, and found that it allowed sugar solution to pass 

 through but Stopped colloidal solutions. The author had used 

 opacity as a test for colloids, but silicic acid could be got trans- 

 parent. There are two kinds of opalescence — one cannot be 

 removed and exists because the substance is a two-phase system ; 

 the other can be removed with difficulty by filtering, and leaves a 

 transparent substance. The want of transparency should be 

 used cautiously as an argument. Dr. Donnan, in reply to Dr. 

 Gladstone's remarks on the transition from crystalloids to col- 

 loids, said that a substance might be a crystalloid with one 

 medium and a colloid with another. In reply to Dr. Lehfeldt, 

 he said that the only evidence in favour of osmotic pressure of 

 colloids is that colloidal solutions diffuse. He agreed with 

 Prof. Threlfall that opacity should be used carefully as an argu- 

 ment, but stated that his theory referred to a two-phase system. 

 — Mr. Appleyard then exhibited three pieces of apparatus. The 

 first was a slide wire bridge for measuring conductivities of 

 wires. The slide wire instead of forming two arms of the 

 bridge forms only one, and the length used is proportional to 

 the conductivity to be measured. If the arm which contains 

 the standard wire used is altered, it becomes necessary to alter 

 the divisions of the scale on the slide wire. This is done by a 

 mechanical arrangement. The second piece of apparatus was a 

 mechanical gauge for measuring the diameters of spheres. The 

 sphere to be measured is placed between a metal face plate and 

 a piece of glass at the end of the short arm of a pivoted lever. 

 The end of the long arm of the lever moves over a graduated 

 scale which is calibrated to show directly the diameter of the 

 sphere. The third piece of apparatus was a galvanometer fitted 

 up for lamp and scale work. The illuriiination was produced by 

 a 4 volt ^-candle power lamp, and it was shown that very good 

 results could be obtained from this by using a large condensing 



NO 1637, VOL. 63] 



lens. Prof. Threlfall said he had usually used a straight piece 

 of the lamp filament itself, instead of using the lamp in con- 

 junction with a cross wire. — A paper, by Prof. R. W. Wood, 

 on the production of a bright line spectrum by anomalous dis- 

 persion and its application to the flash spectrum, was postponed 

 until the next meeting at Burlington House, when the subject 

 will be experimentally illustrated by Mr. Watson. — The Societv 

 then adjourned until March 22, when the meeting will be held 

 in the chemical laboratories of University College, London. 



Geological Society, February 15. — Annual General Meet- 

 ing. — ^J. J. H. Teall, F.R.S., president, in the chair. — It was 

 stated that, the Council having undertaken to supply to the 

 Regional Bureau of the International Catalogue of Scientific 

 Literature the material referring to geology published ■ in the 

 British Islands, Mr. C. Davies Sherborn had been appointed to 

 prepare and edit the catalogue-slips necessary for that purpose. The 

 rejrarts having been adopted, the medals and funds of the Society 

 were awarded as already announced (p. 402) — The president 

 then proceeded to read his anniversary address, in which he 

 first gave obituary notices of several Fellows and Foreign 

 Members deceased since the last annual meeting. He then 

 dealt with the evolution of petrological ideas during the nine- 

 teenth century, especially as regards the igneous rocks. The 

 discussions as to the origin of basalt and granite were referred 

 to, and it was shown that the controversy regarding the latter 

 rock had contributed largely to the clearing up of our ideas as to 

 the nature of plutonic phenomena. The solution-theory pro- 

 pounded by Bunsen was especially emphasised, and its modern 

 developments were briefly sketched. It was suggested that the 

 next great advance will, in all probability, be the result of ex- 

 periment, controlled by the modern theory of solutions, and 

 carried out for the purpose of testing the consequences of that 

 theory and discovering the modifications which may be neces- 

 sary to adapt it to igneous magmas. The bearing which recent 

 work on alloys had on petrographical problems was also referred 

 to. The problem of the origin of petrographical species was 

 next considered, and the growth of ideas on the subject briefly 

 sketched. It was pointed out that although magmatic differ- 

 entiation is accepted by many as an important factor in producing 

 different kinds of igneous rocks, it does not rest on any assured 

 experimental basis. Differentiation dependent on, or connected 

 with, the crystallisation of definite minerals was reviewed more 

 favourably ; but it was pointed out that all theories of differ- 

 entiation which are based on unaided molecular flow are subject 

 to the criticism that the time required to effect any important 

 differentiation appears to be too great. Reference was also 

 made to recent work on the modification of igneous magmas by 

 the inclusion and assimilation of rocks through which they pass ; 

 and the conclusion was reached that the origin of species, so far 

 as igneous rocks are concerned, is a problem the final solution 

 of which has been handed on by the nineteenth century to its 

 successor. 



Royal Astronomical Society, March 8. — Dr. J. W. L. 

 Glaisher, F.R.S., president, in the chair. — Lantern slides 

 were exhibited of photographs of the region of the new 

 star in Perseus, taken by Mr. Stanley Williams. One, taken 

 on February 20, only twenty-eight hours before its discovery, 

 showed no trace of the Nova, though containing stars to about 

 the twelfth magnitude. — Dr. Lockyer showed photographs of 

 the spectrum of the new star, taken at South Kensington. The 

 spectrum showed dark lines of hydrogen, and also broad, bright 

 hydrogen bands displaced towards the red, apparently indicating 

 two sources of light and enormous relative velocities. The 

 spectrum showed the existence in the star of hydrogen, calcium, 

 iron, &c. — Mr. McClean exhibited an enlargement from his 

 photograph of the spectrum, in which he could find no trace of 

 helium. The spectrum of the Nova resembled that of Sirius, 

 but with bright bands of hydrogen ; it was also much like that 

 of Nova Aurigse. — A photograph of the spectrum taken at 

 Stonyhurst was also shown. — Mr. Newall exhibited and ex- 

 plained his photographs of details of the spectrum, taken at 

 Cambridge. — Dr. Rambaut gave results of observations made 

 at Oxford. The colour of the Nova was first of a bluish-white, 

 becoming redder as it diminished in light. — The Astronomer 

 Royal showed photographs taken at the Royal Observatory, 

 where observations were made of the magnitude, which showed 

 a gradual but not perfectly regular, diminution of brightness 

 from 0-5 magnitude on February 25 to 3-1 magnitude on 

 March 6.— Mr. Bellamy brought forward a series of measures 





