April Z^ 1879] 



NATURE 



521 



state, &c.). The hypothesis is advanced, that the ethereal 

 atmosphere condensed round an atom by its attractive action 

 consists of an atmosphere of luminiferous ether, and an envelope 

 of electric ether immersed ^nthin this for a certain depth, an 

 ethereo-electric atmosphere, in fact. — Some observations on 

 fl peculation of small particles (or their tendency to form, under 

 moderate agitation, granular aggregates or compound particles 

 of larger size), are described by Prof. Hilgard, and have 

 important physical and technical bearings, especially on points 

 in agrioilture. — Prof. Dawson points out what he considers 

 defects and errors in the method of investigation pursued by 

 Prof. Mobius recently with regard to Eozoon canadense, leading 

 to a decision adverse to the organic character of that object. — Mr. 

 White offers some remarks on the Jura-trias of Western North 

 America ; Mr. Fontaine continues his notes on the mesozoic 

 strata of Vii^nia, and Mr. Bannister contends for the hypothesis of 

 the transition character of the Rocky Mountain lignite series, or 

 Laramie group. — Some new species of anthozoa and cephalopoda 

 added to the marine fauna of the eastern coast of North 

 America, are described by Prof. Verrill ; the cephalopoda have 

 some specially interesting features. — Mr. Penfield gives analyses of 

 triphylite. 



Annalender PhyHkund Chemie,^o.2. — In this number Herr 

 Thoss communicates an interesting paper on artificial dichroism. 

 He experimented (to produce it) in the three directions of making 

 a coloured isotropous medium doubly refractive, colouring a 

 4oubly-refractive medium, and gi^*ing a colourless isotropous 

 medium both colomr and double refraction. The last series were 

 negative in results. In the first series, plates of gutta-percha, 

 indigo, and chrysamminate of potash gave convincing proof that 

 there is no difference between double refraction produced mechani- 

 cally and double refraction in crystals. It was found impossible to 

 produce dichroism with pressure in coloured glass. Colouring 

 matter in crystals is considered the real producing cause of 

 dichroism. The subject of quickly alternating electric currents 

 is treated by Herr Oberbeck, who notes as an important 

 fact the diminution of the resistance of liquids by increase 

 in the nimiber of alternations of the transmitted current in 

 unit time ; this occurs only when the number becomes high, 

 and the average time of passage of one constituent mole- 

 cule to its neighbour in the direction of the current can 

 ao longer be regarded as infinitely small in comparison 

 to the duration of the current. The author describes experi- 

 ments on alternating currents in two induction coils, variously 

 connected, and finds in the phenomena certain analogies to vibra- 

 tions of the nature of sound and light. — Herr Lubarsch endeavours 

 to show that the faultiness of past experiments on fluorescence 

 has arisen only from the first of three causes assigned by Prof. 

 Lommel, viz.", absorptive action of the fluorescent liquid on the 

 fluorescent light, in observation of the liquid minor. He finds 

 endence of the generality of this law : in all fluorescent sub- 

 stances the more rerran;^ble limit of the derived spectrum coin- 

 cides with the place of strongest absorption in the absorption 

 spectrum, or (where this is not distinctly perceptible) with the 

 place of strongest fluorescence in the fluorescent spectrum. Sub- 

 stances with double fluorescence, as chlorophyll (the phenomena 

 of which he describes), are not excepted from the Law. — Herr 

 Rudorff describes a simple and convenient apparatus for deter- 

 n[iining the specific gravity of powdered substances ; Herr 

 Wiedemann and Herr Schulze, an arrangement with which can 

 be proved the dissociation of hydrate of chloral at 100° ; Herr 

 Wiedemann, experiments yielding the result that by passage of 

 electricity a gas may become luminous far tmder 100°, &c. — A 

 large part of the number is occupied with the concluding part 

 of Kohlrausch's paper on electric conductivity, &c., already 

 referred to. 



Journal de Physiqut, February, 1879. — The opening paper 

 by M. Jamin, on complements to the theory of dew is 

 followed by one in which M. Lippmann shows that the 

 depolarising property of a metallic solution is limited to the 

 same metal as it contains ; and that this electric reaction may be 

 applied, in several cases, in testing for a metal, as a convenient 

 auxiliary of chemical analysis. The electric work expended to 

 produce polarisation is stored (he contends) not in the form of 

 chemical enei^, but in that of electrical, as in a condenser.— 

 M. van der Mensbrugghe offers some remarks on measurement 

 of the superficial tension of liquids, apropos of recent experiments 

 by M. Terquem. — M. Gemez describes a method jof observing 

 the rotatory power of quartz at different temperatures, and which 



seems to meet the difficulties of the case better than that of M. 

 Joubert and other physicists. Two quartzes of contrary rota- 

 tion are fixed at the two ends of a tube, and only one is heated. 

 A universal support or electro-diapason for inscribing and 

 showing in projection vibratory movements is described by M. 

 Duboscq. 



SOCIETIES AND ACADEMIES 

 London 



Royal Society, March 27.—" On the Organisation of the 

 Fossil Plants of the Coal Measures. Part X." By W. C. 

 Williamson, F.R.S., Professor of Natural History in Owens 

 College, Manchester, 



The still existing differences of opinion respecting the botani- 

 cal afl^ities of the Sigillariae give value to every new fact calcu- 

 lated to throw light upon the question. In 1865 Mr. Edward 

 Wunsch, of Glasgow, made a discovery, which proves to have 

 an important bearing upon it. He found, at Laggan Bay, in 

 Arran, a series of rather thin carboniferous strata, separated by 

 thick beds of volcanic ash, and in one of the carboniferous shales 

 especially, he discovered the bases of the stems of numerous 

 very large trees standing perpendicularly to the shales. These 

 trees have been referred to by several authors as Sigillarian. In 

 the summer of 1877 Mr. Wtmsch and I employed quarrjinen to 

 make extensive excavations amongst these strata, for the ptirpose of 

 adding to the extensive series of specimens which he had obtained, 

 and the whole of which he kindly placed in my hands. The 

 aggregate result of these explorations was to show that the con- 

 clusion previously arrived at, \\z., that the stems had belonged 

 to a grove of Sigillarian trees, was unsupported by a solitary 

 fact. These stems were of very large size, showing that they 

 had belonged to fully grown trees. None of them displayed any 

 traces of leaf -scars, having outgrown the stages at which such 

 scars would remain visible. Their outer surfaces were scored 

 with deep irregular longitudinal fissures, resulting from internal 

 growth and consequent expansion, and which appear to have 

 been mistaken for die lon^tudinal grooves and ridges of a Sigil- 

 larian bark. Such, however, they certainly were not, since, in 

 every instance, the surface bark had been entirely thrown off, 

 and the fissures entered deeply into the subjacent b^k layer. In 

 most of the stems this comparatively thin bark layer was the 

 only one that remained, the greater portion of the inner bark 

 and the central vascular axis ha^-ing disappeared, leaving a large 

 cylindrical cavity, which was filled up with volcanic ash. These 

 stems failed to display a single feature justifying the conclusion 

 that they were Sigillarian, 



In two of them the central cavity, instead of being filled with 

 ash, was filled with [miscellaneous heaps of vegetable matter, 

 amongst which were large fragments of the vascular axes of 

 various plants, such as Lepidodendra and Stigmariae, but in one 

 of the largest stems were five or six decorticated vascular cylin- 

 ders of Diploxyloid stems, of the largest size, and which, though 

 arranged parallel to the long axis of the cylinder which inclosed 

 them, obviously did not belong to them, but had been floated in 

 from >vithout. The supposition that these had been young 

 stems that had grown within the hollow protecting cylinders, 

 fi-om spores, accidentally introduced, is wholly untenable, since 

 each one of these several vascular axes lias been the centre of a 

 stem fully as large as that within which we found them aggre- 

 gated. Of course, these Diploxyloid vascular axes had the 

 organisation which Brongniart and the younger school of French 

 botanists which still upholds his %'iews on this point, believe to 

 be characteristic of true Sigillariae — a conclusion from which I 

 have long dissented. 



The only fragments we found, that threw any light upon the 

 character of the leaf-scars that had indented the surfaces of 

 these fiflly-grown stems, was a well-defined example of the 

 Lepidodendroid type. 



We directed careful attention to the nature of the smaller 

 fragments of branches and foliage which abounded in the vol- 

 canic ash with which the large stems were overlaid. These 

 consisted of Lepidodendroid branches and twigs of all sizes and 

 ages, and no doubt was left upon my mind that they were really 

 the disjecta membra of the stems around which they were so pro- 

 fusely scattered. The only fruits that have been obtained from 

 the same locality are Lepidostrobi, most of which contain 

 macrospores and microspores. Unless we »re prepared to 

 believe that this Arran deposit contained, on the one hand. 



