302 



NATURE 



\Aug. 3, 1876 



yielding so many interesting and striking results. — The Mine- 

 ralogische Mittheilungen, which, under the editorsnip of Dr. 

 Tschermak now forms such a vahiable portion of the Jahrbuch, 

 contains an article by Dr. Hirschwald " Zur Kritik des Leucit- 

 systems," which is sure to he eagerly read, now that so much 

 attention has been excited on this question by the memoirs of 

 von Rath and Scacchi. — Dr. Brezina's contribution to the question 

 of isomorphism, especially in its bearing on the classification of 

 the felspars, is not yet completed, but promises to be one of 

 great importance and suggestiveness. — Dr. Drasche, who, on his 

 way to the Malay Archipelago, whither he is gone to study the 

 volcanic phenomena of that area, has visited the island of 

 Bourbon, sends home an interesting communication concern- 

 ing its geology, which is also published in the Mineralogische 

 MiUheilungen, 



Gazzetta Chimica Italiana, Anno vi. 1876, fasc. iii. — A con- 

 siderable poition of this number is taken up by an account of 

 the researches of E. Patemo, of the University of Palermo, on 

 usnic acid as derived from Zeora sordida. His investigations 

 induce him to adopt the formula CijHigOy in preference to 

 those adopted by Stenhouse, Hesse, and others who have 

 interested themselves in this body. In deriving usnic acid from 

 the above source, the investigator discovered two new substances 

 which were invariably present, although in exceedingly small 

 quantities. To these he has given the names zeorin and sordidin 

 (zeorina e sordidina), and assigned the formulae CuH^.^O to the 

 former, and CigH,g07 to the latter. — G. Koemer contributes a 

 paper on the constitution of veratric acid and veratroL The 

 same investigator, conjointly with G. Monselise gives an interest- 

 ing account of two benzol-bisulphuric acids, and of their rela- 

 tions with other compounds. — In addition to the foregoing, an 

 extract from an account of Prof. F. Selmi's research on atropine 

 is given, and a paper by R. Schiff on the product obtained by 

 bringing into contact with each other acetylic chloride and acetic 

 aldehyde.— F. Sestini furnishes a paper on ethyl santonate, and 

 a few extracts from other chemical journals complete this serial. 



Journal de Physique, April. — M. Cazin here gives an outline 

 of his recent researches on the thermal effects of magnetism. 

 The three methods are described by which he measured the 

 calorific effects produced in the core, also his mode of measuring 

 the magnetic quantities, with the electrodynamic balance. In 

 the case of a bi-polar tubular core, the quantity of magnetism 

 alone being varied, by changing the intensity of the current, the 

 quantities of heat generated by intermittences of the current are 

 proportional to the squares of the quantities of magnetism alter- 

 nately gained and lost by the core. The polar interval alone 

 being varied, by altering the length of the core, the quantities of 

 magnetic heat are proportional to the polar intervals, and con- 

 sequently to the magnetic moments. In the case of a multi-. 

 polar tubular core, the successive polar intervals being equal, 

 the quantities of heat generated in the core by the same inter- 

 rupted current are inversely proportional to the squares of the 

 number of intervals. — The Bureau des Longitudes decided in 

 May last year to rectify annually the Magnetic Map of France ; 

 and in this number are shown the isogonic lines, degree by 

 degree, as deduced from last year's observations. There is also 

 a table of the principal towns in France, with the declination 

 and annual variation for each. — A note by M. Potier treats of 

 the conveyance of luminous waves by ponderable matter in 

 motion. — We further note an abstract ot researches by MM. 

 Angstrom and Thalen, on the spectra of the metalloids. They 

 affirm that carbon has only one spectrum, a spectrum of lines j 

 the other spectra attributed to it are due to compound bodies. 

 The same with nitrogen. 



SOCIETIES AND ACADEMIES 



London 



Geological Society, June 21.^ — Prof. P. Martin Duncan, 

 F.R.S., president, in the chair. — 12. On the mechanism of 

 production of volcanic dykes and on those of Monte Somma, 

 by R. Mallet, F.R.S. The author stated that in 1864 he 

 made a careful trigonometrical survey of the escarpment of 

 Monte Somma, especially with reference to the numerous 

 dykes by which the rocks composing it are intersected. He 

 described in detail the phenomena of direction of the dykes, 

 especially as regards the axis of the cone of Vesuvius ; to this 

 direction he gives the name of orientation. Of twenty-seven 



» Continued from p. 282. 



dykes ten presented an approximately vertical line, whilst all the 

 rest had a sensible dip cr *' hade." The dykes are in no cases 

 intersected by coherent beds of lava, but in one instance the top 

 of a dyke was stopped by such a bed. Many of the dykes bifur- 

 cated or branched, and frequently two dykes intersected each 

 other at considerable angles. These and other circumstances 

 prove that the dykes were produced at different and successive 

 ages. Many of them were fractured and displaced in consequence 

 of movements of the mass of rock traversed by them ; and these 

 dislocations are regarded by the author as indicating the vast 

 extent and force of the internal movements, due principally to 

 gravity, which are constantly taking place in the mass of volcanic 

 cones. These movements greatly influence the position of the 

 dykes, and render it difficult to ascertain that which they origin- 

 ally occupied. The dykes thin out at various heights, and their 

 superior and northern terminations were found not to reach the 

 existing surface, notwithstanding the amount of denudation that 

 has taken place ; and hence the author concludes that they never 

 reached the surface of Somma, when it was the wall of an active 

 volcano. The author further indicated a process by which beds 

 or plates of lava descending the slopes of a volcano may change 

 their direction, and becoming embedded in the detritus accom- 

 panying or following them, may, to a greater or less extent, 

 simulate dykes, although in this case the two sides of the plate 

 will present the differences always seen in the upper and under 

 surfaces of a bed of lava. The orientation-lines of five or six 

 of the observed dykes were said to pass approximately through 

 the axis of the cone of Vesuvius, but all the rest presented great 

 diversities, and some, when prolonged, would not touch the cone 

 at all. In making a lithological examination of the dykes of 

 Somma, the author directed particular attention to the position 

 of the elongated air-bubbles found in the material of each dyke, 

 considering that the direction of the longest axis of these bubbles 

 would indicate the flow of the material when in fusion. He 

 stated that on the whole the long axes of the bubbles are nearly 

 horizontal or pointing at moderate angles upwards in directions 

 very nearly parallel to the plane of the dykes at the place where 

 they occur. Hence he inferred that the dykes were filled by 

 injection not from below but nearly horizontally. The author 

 further referred to the mineralogical characters of the materials 

 of the dykes, and stated that they are not all composed of leucitic 

 lava ; he also mentioned the occurrence of cross columnar struc- 

 ture in some of the larger ones. After referring to the differences 

 observable in the physical condition of the two surfaces of some 

 dykes, the author proceeded to consider the mode of origin of the 

 fissures, which, when filled, constitute volcanic dykes. He main- 

 tained that the production of a fissure and its filling with molten 

 matter must have been simultaneous and due to the same cause, 

 namely, the hydrostatic pressure of the liquid lava more or less 

 filling the crater, the pressure originating the fissure into which 

 the pressing liquid at the same time enters ; a fissure thus pro- 

 duced and filled will always be widest near the crater, so that if 

 the material of the cone were perfectly uniform the dykes pro- 

 duced will be wedge-shaped. But from the absence of this 

 uniformity and other causes, fissures commenced at the interior 

 and propagated into the mass of volcanic cones can rarely be 

 uniformly distributed round the crater or produced in regular 

 vertical planes in a truly radial direction. Hence the author 

 concluded that it is unsafe to attempt to fix the position of an 

 ancient crater by means of the intersection or concurrence of the 

 lines of apparent orientation of dykes alone. The author stated 

 that the intrusion of volcanic dykes cannot so greatly influence 

 the slope of volcanic mountains as has been supposed. — 13. On 

 the metamorphic rocks surrounding the Land's End mass of 

 granite, by S. AUport. In this paper the author described 

 the results of a microscopic examination of certain meta- 

 morphic rocks surrounding the Land's End granite, indi- 

 cating the changes produced by the intrusion of the latter 

 upon clay slate and upon certain igneous rocks. The slates 

 in contact with granite become converted into tourmaline- 

 and mica-schists, and are found to contain crystalline quartz, 

 tourmaline, and three distinct varieties of mica, with occasion- 

 ally tremalite, magnetite (and andalusite ?), and in some localities 

 felspar. Their structure is also changed, the most remarkable 

 changes being foliation with every gradation from nearly straight 

 parallel lines to the most complicated contortions, and concre- 

 tionary structure by segregation of quartz and mica, the result 

 being a spotted schist. With regard to the origin of the granite 

 of Cornwall, the author said that neither observation in the field 

 nor microscopical study lends any support to the notion that it is 

 a metamorphic rock ; but, on the contrary, that there is the 



