May 25, 1876] 



NATURE 



83 



Geologists' Association, April 7, — Mr. Wm. Carruthers, 

 F.R.S., president, in the chair. — On the volcanoes of Iceland, 

 with special reference to those mountains which have recently 

 erupted, by W. L. Watts. The vast mass of the Vatna-Jokull 

 rests upon a base of tuff and agglomerate traversed in many 

 places by intruded basaltic and other lavas. This mountain and 

 its immediate neighbours constitute the highest and probably the 

 oldest part of Iceland, for its lava streams are in a state of ruin 

 and decay unequalled in any other part of the country, and it is 

 girt upon its southern base by sea- cliffs, which must have been 

 washed by the ocean when many other parts of Iceland were 

 under water, unless a very serious depression has taken place 

 since the southern outlying hills of the Vatna and Skaptar Jokulls 

 were washed by the sea. The fires in the Vatna are not yet extinct. 

 Crossing the deserts to the north of the Vatna Jokull, on the 

 west is a large tract of lava, the greater part of which has flowed 

 from Skaldbreith ; whilst in front rise the DyngjufjoU or Cham- 

 ber Mountains, the volcanoes which caused so much damage 

 to the north of Iceland last spring. These mountains are com- 

 posed of palagonitic agglomerate, and are in many places tra- 

 versed by dykes and masses of lava, whilst numerous protruding 

 scoriaceous crags suggest that lava streams may lie beneath. 

 The sides have been fissured and cracked by the violent earth- 

 quakes which preceded the eruption of last spring. In the lati- 

 tude of 64° 45' N. , and extending eastward towards the sea 

 shore, the country was found to be strewn with a light vitreous 

 pumice, very vesicular, and assuming most beautiful shapes. The 

 crater from which this was ejected is situated in the south corner 

 of the Askja (oval wooden casket), the name given to an elevated 

 piece of land enclosed upon all sides but the north-east by semi- 

 detached sections of mountains. The fissures in this volcano 

 were still in active eruption, sending forth vast volumes of steam, 

 a dark granulated fetid earth which occasionally fell around in 

 showers, and a little water. Copious floods of water had flowed 

 down the sides of the volcano ; this is the more remarkable, as 

 the Dyngjufjolls are neither glacial nor snow-capped mountains. 

 The Oskja-gja (chasm of the oval wooden casket) is, moreover, 

 at least thirty-eight geographical miles from the lake of Myvatn, 

 and forty-five from the nearest sea-shore. The second centre of 

 recent volcanic activity is situated in the Myvatns Oro^fi, where 

 the volcanic fires first made their appearance last year. After 

 the violent earthquakes which at Christmas, 1873, shook the 

 north-east of Iceland, a fissure twelve miles in length, and vary- 

 ing from one to thirty feet in breadth, opened in the west portion 

 of the Myvatns Oroefi, and commenced to eject lava from four- 

 teen or fifteen different points. Many of the smaller fissures 

 formed by these earthquakes casfup stones and ashes, and lava 

 welled up through them. The great discharge of lava, how- 

 ever, was from the great fissure, which formed a lava streani 

 some thirteen miles in length, and varying from one to tliree in 

 breadth ; it has ovei flowed an older lava stream which had issued 

 from a vent in the Myvatns Ora-fi, called the Svinagja. This 

 fissure broke out again in March, and continued in a state of 

 intermittent activity until the following April. The lava is 

 basaltic, and differs from the ancient streams only in its not 

 containing olivine. The fundamental rock of Iceland is the 

 palagonitic tufa of sub-aqueous origin, disturbed and at times meta- 

 morphosed by enormous masses of amygaloidal basaltic lava ; 

 these are overlaid by sub- aerial lava streams, pumiceous tuffs, 

 and agglomerates which have been formed by debacles and 

 atmospheric influences. Trachytic lavas occur but sparingly, 

 the trachytic band supposed to bisect the island from Cape 

 Langaness to Rejkjaness being unsupported by investigation. 

 Trachytes in a much altered condition have been found around 

 and between Hekler and the geysers. Obsidian is seldom met 

 with in situ ; Mount Paul, however, in the heart of the Vatna 

 Jokull, consists of this rock, whilst the pumiceous outburst of 

 the Oskja-gja must also be referred to it. 



May 5.— Prof. J. Morris, F.G.S., vice-president, in the chair. 

 —On the section of the chloritic marl and upper greensand on 

 the northern side of Swanage Bay, by H. George Fordham, 

 F.G.S. — Notes on the geology of the neighbourhood of Swan- 

 age, by W. R. Brodie. 



Institution of Civil Engineers, May 9.— Mr. W. II. 

 Barlow, vice-president, in the chair.— The first paper read was 

 on the construction of railway wagons, with special reference to 

 economy in dead weight, by W. R. Browne, Assoc. Inst. CE.— 

 ihe second paper read was on railway rolling-stock capacity, in 

 relation to the dead weight of vehicles," by Mr. W. A. Adams, 

 Assoc. Inst. CE. 



Cambridge 

 Philosophical Society, Feb. 28.— The following communi- 

 cation was made to the Society by Prof. Clerk Maxwell, on 

 Bow's method of drawing diagrams in graphical statics, with 

 illustrations from Peaucellier's cell :— A frame is a structure con« 

 sisting of pieces jointed together at their extremities. India- 

 grams the joints are represented by points, and the pieces by 

 straight lines joining the points. A diagram of stress is a figure 

 such that the forces acting at each joint of the frame are repre- 

 sented in direction and magnitude by the sides of a polygon 

 in the diagram of stress. When the diagram of stress is such 

 that to the lines which meet in a point in the diagram correspond 

 the sides of a polygon in the frame, the frame and the diagram 

 are said to be reciprocal. Mr. R. II. Bow, C.E., F.R.S.E., in his 

 " Economics of Construction in relation to Framed Structures," 

 has pointed out a method of constructing reciprocal diagram! 

 which applies to cases which I had formerly thought imprac* 

 ticable. Mr. Bow assigns a letter to each enclosed space of the 

 frame, and also to each division of the surrounding space as 

 separated by the lines of action of the external forces. _ When 

 two pieces of the frame cross each other without being jointed, 

 Mr. Bow treats them as if they were jointed. The forces at the 

 point of intersection are represented by a parallelogram. In the 

 diagram of stress the letters are placed at the points which cor« 

 respond to the enclosed spaces of the frame. In Peaucellier's 

 cell the three external forces acting at the centre and the two 

 bracing points meet in a point in the diagonal through the other 

 two angles of the rhombus. To every positive cell in which the 

 centre is outside the rhombus corresponds a negative cell in which 

 the centre is inside the rhombus, and if the point of concourse of 

 the forces is outside the rhombus in one case it is inside in the 

 other. Every line in the one figure is parallel to the corre« 

 sponding line in the other, and the only difference is that the 

 acute angles of the rhombus, in one figure correspond to the 

 obtuse angles in the other. These two frames have the same 

 diagram of stress, so that the stress of corresponding pieces ia the 

 two frames is the same. 



March 23.— Mr. Pearson made a communication on a set of 

 lunar distances taken by him under rather peculiar circumstances 

 last autumn, Oct. 8. 



March 27. — Mr. Anningson read a paper on the relation of 

 the spinal cord to the tail in mammals.— On vital force, by Mr. 

 H. F. Baxter. 



Manchester 

 Literary and Philosophical Society, Feb. 22.— Mr. E. 

 Schunck, F.R.S., president, in the chair.— Notes on a collection 

 of apparatus employed by Dr. Dalton in his researches, which is 

 about to be exhibited (by the Council of the Literary and Philo- 

 sophical Society of Manchester) at the Loan Exhibition of Scien- 

 tific Apparatus at South Kensington, by Prof. Roscoe, F.R.S. — 

 A letter from Mr. Arthur Wm. Waters, dated Naples, Feb. 9, 

 1876, was read by Mr. Baxendell, giving some account of the 

 Naples Zoological Station.— On glacial action in the valley of 

 the Wear, &c., by Prof. T. S. Aldis. 



Feb. 29.— E. W. Binney, F.R.S., in the chair.— An account 

 of some early experiments with ozone, and remarks upon its 

 electrical origin, by J. B. Dancer, F.R. A. S.— Results of rain- 

 gauge observations made at Eccles, near Manchester, during the 

 year 1875, by Thomas Mackereth, F.R. A.S. 



March 7.— Mr. E. Schunck, F.R.S., president, in the chair.— 

 Mr. R. S. Dale exhibited specimens of crystals of sulphate of 

 lead found in alum residue,— On the degree of accuracy dis- 

 played by druggists in the dispensing of physicians' prescriptions 

 in different towns throughout England and Scotland, by. Mr. 

 William Thomson, F.C.S. , . 



March 13.— Prof. W. Boyd Dawkins, F.R.S. in the chain- 

 Mr. Charles Bailey exhibited a series of slides illustrating simi- 

 larities of structure in Dicotyledonous and Monocotyledonous 

 stems.— Mr. R. D. Darbishire, F.G.S., exhibited a series of 

 specimens of very young Rhombus vulgaris (Cuv.), showing (i), 

 the two eyes on each side of the vertebral plane ; (2), the removal 

 of the eye from the underside to the dorsal edge ; (3), the appear- 

 ance of both eyes on the one (upper) side of the fish. He also 

 communicated some notes made during a visit in the past summer 

 to the Swedish shell-beds of Uddevalia and the neighbouring 

 district, and exhibited a collection of the fossils of remarkable 

 extent and beauty.— List of shells found in Cymmeran Bay, 

 Anglesea. Corrections and additions, by Mr. John Plant, F.G.S. 

 Addenda and corrigenda. 

 March 21.— Mr. E. Schunck, F.R.S., president, in the chair. 



