December 7, 1H93] 



NA rURE 



U3 



having the composition of the average olivine-gabbro-diabase. 

 The petrographical variations, such as the occurrence of pyroxy- 

 enites and augite-dioriles, in the plutonic masses themselves are 

 described, and attributed to differentiation under physical condi- 

 tions unlike those which gave rise to the camptonites and 

 bostonites. In discussing the general laws of differentiation 

 the author pointed out that it must have taken place before 

 crystallisation to any extent had occurred, because there is a 

 marked difference in mineralogical composition between the 

 rocks occurring as bosses and those occurring as dykes : and, 

 further, that it is dependent on the laws which determine the 

 sequence of crystal-building, in so far as the compounds which, 

 on given conditions, would first crystallise are those which have 

 diffused to the cooling margin, and so produced a contact- 

 stratum, of peculiar chemical composition, before any crystal- 

 lisation had taken place. A discussion followed, in which the 

 President, Prof. Judd, General McMahon, Prof. J. F. Blake, 

 and Mr. W. W. Watts took part. — On the sequence of perlitic 

 and spherulitic structures (a rejoinder to criticism), by Mr. Frank 

 Rutley. This paper related to the order in which the perlitic 

 and spherulitic structures have been developed in a felsitic lava 

 of Ordovician age from Long Sleddale, Westmoreland. The 

 author having described this rock in a paper published in the 

 Quarferly Journal of the Society in 1884, and the accuracy of 

 the views then expressed having been questioned, endeavoured 

 to confirm his original statements, adducing in support fresh 

 observations made upon this and other rocks of a similar kind. 

 Mr. Marr and Dr. J. W. Gregory spoke on the subject of the 

 paper, and the author briefly replied. — Enclosures of quartz in 

 lava of Stromboli, &c. , and the changes in composition pro- 

 duced by them, by Prof. H. J. Johnston-Lavis. The author 

 described the existence of enclosures of quartz in a lava-stream 

 at the Punta Petrazza on the east sile of Stromboli, and also 

 in the rock of the neck of Strombolicchio. He described the 

 effects of the rocks upon the enclosures, concluding that the 

 quartz has undergone fluxion but not fusion, and has supplied 

 silica to the containing lavas, thus causing an increase in the 

 amount of pyroxene and a diminution in the amount of mag- 

 netite in the portions of those lavas that surround the inclusions 

 and raising the percentage of silica. He suggested that such a 

 process at greater depths and higher temperature may, under 

 certain conditions, convert a basic rock into a more acid one, 

 so that possibly the andeshe of Strombolicchio may have been 

 of basaltic character at an earlier period of its progress towards 

 the surface. He offered the sugge>tion that other rocks or 

 minerals once associated with the quartz have been assimilated 

 by the magma. The President and Prof. Judd made a few re- 

 marks upon the paper. 



Cambridge. 

 Philosophical Society, October 30. — Prof. Hughes, Presi- 

 dent, in the chair. — The following officers were elected for the 

 ensuing session : — Pre>ident, Prof. Hughes ; Vice-Presidents, 

 Prof. C'ayley, Prof. Darwin, Dr. A. Hill ; Treasurer, Mr. 

 Glazebrook ; Secretaries, Mr. Larmor, Mr. Newall, Mr. Bate- 

 son ; New Members of Council, Prof. Sir G. G. Stokes, Dr. 

 Lea, Mr. Shipley, Mr. Seward. — The President (Prof. Hughes) 

 read a paper on the geological evidence for the recurrence of 

 ice ages. Prof. Hughes pointed out that the advocates of the 

 astronomical explanation of glacial ages have urged that there 

 has been a recurrence at rt-gularly varied intervals of combina- 

 tions, the result of which must have been circum polar vicissi- 

 tudes of climate ; and, seeing that the secular recurrence of 

 these conditions formed a necessary part of their theory, they 

 gladly welcomed any confirmation of it, such as was offered by 

 those geologists who saw in the character of the stones in cer- 

 tain conglomerates traces of ice-action in several successive 

 geological periods. The value of this evidence he now criti- 

 cised. He laid before the Society examples of the striated 

 boulders and rock floors supposed to present glaciated surfaces, 

 and with a view to the elimination of sources of error in the 

 identification of the work of ice he exhibited a large series of 

 specimens illustrating the various ways in which results were 

 produced sometimes exactly the same as, and often closely re- 

 sem.bling, the forms, markings, and other characters relied 

 upon as proofs of ice action. By reference to these he showed 

 that the facetted stones from which the extension of the glacial 

 conditions over parts of Southern Germany was inferred, 

 found their exact counterparts among those trimmed by blown 

 sand intii roof-like forms and ridges, and had no parallel among 

 undoubtedly glacially-dressed stones. The scratched stones in 



the base of the New Red, or so-called Permian of England 

 (with the exception of one single specimen, which he said must 

 have got into the collection in Jermyn Street by mistake,, he 

 compared with those produced by earth movements, in which 

 the included pebbles of the conglomerate were protruded through 

 the softer matrix and scored and indented by harder fragm.ents 

 held in the mass. The supposed glaciation of the boulders in 

 the basement beds of the carbonilerous he explained in the 

 same way, producing examples in which the matrix and in- 

 cluded fragments were scored alike by movements along small 

 fault faces. He exhibited a portion of the solid silurian floor 

 on which these conglomerates rested, which was striated in a 

 manner that might be easily mistaken for glacial action ; but 

 he explained that he had taken this from a thrust plane, and 

 he pointed out the difference in the mineral condition of the 

 surface between these slickensided surfaces and those produced 

 by glacial action. He excluded from the present discussion 

 cases in which ice agency was inferred only from the size and 

 shape of the stones or their isolation in finest material. He 

 admitted the probability of evidence of ice action being found 

 along known axes of recurrent upheaval, such as those in the 

 most ancient rocks along the Scandinavian range, or in the 

 more recent deposits along the Alpine chain, or further south 

 in the carboniferous boulder beds of India, Africa, and Aus- 

 tralia ; but he pointed out that these last, at any rate, could 

 lend no support to the astronomer's contention, seeing that 

 they surrounded a basin whose centre was in equatorial, not in 

 circumpolar regions. He was willing to admit that in the 

 astronomical combinations we might find a vera causa of vicissi- 

 tudes of climate, but he urged that all the evidence from direct 

 observation went to show that extreme glaciation does and did 

 always bear a direct relation to earth movements. 



Paris. 



Academy of Sciences, November 27. — M. de Lacaze- 

 Duthiers in the chair. — On the registration of the variable 

 elements of the sun, by M. H. Deslandres. — On equations and 

 implicit functions, by M. Pellet. — On surfaces admitting of 

 gauche cubics for asymptotic lines, by M. Blutel. — On ripples- 

 {clapotis), by M. E. Guyou. Equations are obtained in which 

 elliptic functions are substituted for the circular functions em- 

 ployed by Boussinesq. According to these equations, each 

 molecule oscillates along a straight line of fixed direction which 

 itselt oscillates vertically, and the resultant motion takes place 

 along a parabola whose axis is vertical. For the surface 

 molecules, the first movement is that of the projection upon the 

 minor axis of an ellipse of a point describing the contour of the 

 curve with a constant linear velocity. On examining the photo- 

 graphic tracing obtained by M. Marey it is found that the 

 motion of the surface molecules takes place along a very flat 

 closed curve. This divergence from the theory is easily ex- 

 plained by the oscillations of the cylinder producing in the 

 experimental basin a vertical displacement of the layers which 

 are theoretically at rest. The superposition of this motion upon 

 that indicated by the theory has the effect of separating 

 in a vertical sense the trajectories corresponding to the two 

 inverse phases of an oscillation. — Mutual action of bodies 

 vibrating in fluid media, by MM. Berson and Juppont. Two 

 vertical discs were placed in air with their axes coincident. 

 The one was made of steel, 0033 cm. thick and 12 cm. in 

 diameter, and was kept vibrating by two small electromagnets, 

 excited by currents of intensities, varying according to the 

 amplitudes required. The other w"as of mica, 0'012 cm. thick 

 and 6 cm. in diameter, fixed normally to the bent end of a 

 light bar of aluminium, which, supported by a long silver wire, 

 formed the movable part of a torsion balance. The movement 

 of this disc is due to the surrounding air, thus being analogous 

 to electrostatic induction. The experiments were made inside a 

 cage draped with soft and loose cloth, to prevent resonance. The 

 torsion was measured with a Vernier micrometer to Jt degree. 

 The attractions exhibited between the two discs when vibrating 

 ranged from half a dyne to about 600 dynes. At a distance 

 of I mm. it was 6o2"3 dynes; at 2 mm., gS'o; at 4mm., 

 14-5, and at 10 mm., 2 '55. To produce the same forces 

 electrostatically, a difference of potential of 600 volts would be 

 required. The authors intend to study the effect of distance 

 and of the medium in the case of pulsating spheres. — 

 Calculation of the forces to which bodies placed in an electro- 

 magnetic field are subjected, by M. Vaschy. — On the variation 

 of the electric state of the high atmospheric regions in good 



NO. 1258, VOL. 49] 



