ymic 14, 1877J 



NATURE 



135 



— On the structure and affinities of the genus Siphonia, by W. 

 J. SoUas, F. G. S/ This paper contained, first, a full account of 

 the history of the genus Siphonia, including a complete list of 

 its described species, and, next, a description of its general and 

 minute structure. Its skeletal network was shown to consist of 

 spicular elements belonging to the Lithistid type of sponges, and 

 most closely allied in generic details to the recent form Disto- 

 dervtia polydisctis. Not only in this character but in every other, 

 Siphonia was shoA-n to approach Discodcrmia so closely as to be 

 almost identical with it. The mineral replacements which have 

 affected the siliceous skeleton of Siphonia were then considered. 

 The paper concluded with a systematic description of the genus. — 

 On the serpentine and associated rocks of the Lizard district, by 

 Rev. T. G. Bonney, F.G.S., fellow and late tutor of St. John's 

 College, Cambridge. The author stated that considerable doubt 

 appeared still to exiit as to the true relations of the lizard ser- 

 pentine and the associated hornblende schists, and as to the 

 origin of the serpentine. He had carefully examined all the 

 junctions accessible on the Cornish coast (inland they are gene- 

 rally obscured). Some of them are concealed by di/>ris, &c., 

 but the majority prove beyond doubt that the serpentine is in- 

 trusive. Further, almost everywhere large fragments of horn- 

 blende schist are caught up and included in the serpentine. Be- 

 sides the serpentine there is a large mass of gabbro at Crousa 

 Down, and many dykes and veins along the east coast almost to the 

 extremity of the serpentine region. At Coverack Cove, near the 

 above mass, are gabbros of two ages, the older much resembling 

 a kind of troktolite. On microscopic examination it proves to 

 be chiefly plagioclase felspar, augitic minerals (including dial- 

 lage), and olivine partially converted into serpentine. There is 

 a red and a green variety. The newer, a coarser variety, ap- 

 pears to be of the same age as the other veins on the coast, and 

 connected with the main mass. Some remarkable changes have 

 taken place in this also. In certain places it exhibits a separa- 

 tion of its mineral constituents, causing it to resemble a foliated 

 rock. This is proved to be due to pressure at right angles to 

 the structure. The minerals also are often changed. The fel- 

 spar is replaced by a white granular mineral resembling saus- 

 surite ; the diallage (which occurs sometimes in very large 

 crystals) is often partially, or even wholly, converted into rather 

 minute crystalline hornblende. In these specimens there is no 

 olivine to be distinguished. The great mass, however, is rich in 

 olivine, yet a weathered specimen from if, resemblmg in aspect 

 the gabbro of the veins, does not show olivine. Hence the 

 author believes that in certain cases the olivine, instead of being 

 converted into serpentine, aids in forming the hornblende. 

 Further, there are dykes and veins over the same area of a dark 

 trap. Some of these are augitic, others hornblendic. The 

 author believes that at any rate in certain of these the horn- 

 blende is of secondary formation. On the west coast are veins of 

 granite ; those on the east coast, said to be granite, prove, on 

 careful examination, to be altered rock, remarkably like granite 

 veins, but not really such. In discussing the origin of the ser- 

 pentine the author called attention to a structure commonly seen, 

 which appeared to be a true " fluidal structure." He then de- 

 scribed the result of microscopic examination of many specimens of 

 the lizard and some other serpentines. Commencing with slightly 

 altered Iherzolite (from the Ariege), he traced the change through 

 the older gabbro of Coverack to the serpentine rock of that place, 

 which contains a large quantity of unaltered olivine ; and so to 

 other serpentines in which the olivine is quite replaced by the 

 mineral serpentine. He described also the mode of the change. 

 The other minerals found in the serpentine rock are enstatite, 

 varieties of augite, and occasionally a fair quantity of picotite, 

 with, of course, oxides of iron. Hence he concluded that, as 

 had been already shown as regards some other serpentines, that 

 of the lizard was the result of the hydrous alteration of an olivine 

 rock, such as Iherzolite. — On certain ancient devitrified pitch- 

 stones and perlites from the Lower Silurian district of Shrop- 

 shire, by S. AUport, F.G.S. 



Physical Society, June 9. — Prof G. C. Foster, president, 

 in the chair. — The following candidates were elected members 

 of the Society :— Mr. W. H. Northcott and Mr. L. J. Whalley. 

 — Mr. S. r. Thompson read a paper on interference fiinges 

 within the Nicol prism. After referring to the original paper 

 by the inventor in 1S2S, in which this phenomenon was referred 

 to, he gave a general description of it prior to explaining the 

 cause. If the " field " of a Nicol be explored by the eye it will 

 be seen to be bordered on one side by a margin of violet-blue 

 light, and on the other, when the light passes obliquely through 



the prism, by an orange band within which lie a series of coloured 

 fringes ; these latter are very clearly seen with monochromatic 

 light, when a second set, within the blue band, also appears. 

 The author showed that these two sets are due to intetference 

 taking place within the film of balsam at the critical angle of 

 total reflexion for ordinary and extraordinary rays respectively ; 

 they are therefore analogous to the interference bands in a thin 

 film, placed beneath a prism of a more highly refracting sub- 

 stance and occurring just within the limit of total internal reflec- 

 tion, as first observed by Sir \V. Herschel. At the conclusion 

 of the scientific business of the Society, a special general meeting 

 was held. 



Royal Microscopical Society, June 6. — Dr. Rnbt. Braith- 

 waite, vice-president, in the chair. — Six new fellows were 

 elected, and M. L'Abbc Renard was elected an honorary fellow 

 of the Society. — A paper by the Rev. J. Delsaulx on the thermo- 

 dynamic origin of the Brownian motion was read by the secre- 

 tary, and described the observations of the author with regard to 

 the motion of fluid in rock cavities and molecular motiorr gene- 

 rally, with a view to establish the theory that it was due to the 

 action of temperature. The observations had been suggested by 

 the study of Crookes's radiometer. — A letter I'rom Mr. H. C. 

 Sorby on the subject was also read to the meeting, and Mr. 

 Hartley described his experiments which led to the same conclu- 

 sions. The meeting was then adjourned until October. 



Edinburgh 

 Royal Society, June 4. — Prof Kelland in the chair. — SirC. 

 Wyville Thomson read a paper on the structure and relations of 

 the genus Holypus. — Mr. Alexander Buchan, M.A., secretary 

 to tire Scottish Meteorological Society, communicated the second 

 part of his investigations of the diurnal oscillations of the baro- 

 meter. He stated that the summer months of the northern 

 hemisphere as indicated by the barometer were May, June, and 

 July, the winter months being November, December, and 

 January, both corresponding with the sun's declination. He 

 has now results of the daily barometric readings from upwards 

 of no stations at dilTerent parts of the earth's surface. His in- 

 vestigations showed that a long-contmued series of observations 

 was absoliitely necessary to show the peculiarities of the baro- 

 metric curve. For instance, three years' observations gave in 

 the case of Great Britain only the broadest characteristics. He 

 found that no theory as yet propounded would explain the 

 diunral oscillations of the barometer, and that as more facts were 

 obtained the difficulty of framing a satisfactory theory was greatly 

 increased. — In his paper on the air dissolved in sea-water, Mr. 

 J. Y. Buchanan stated that the result of the analysis he has as 

 yet made of the specimens of the air dissolved in sea- water which 

 were collected in the recent C/zn/Zew^fr expedition, tends to show 

 that as regards surface-water least air was dissolved where the 

 temperature was highest, e.g., near the equator, and most where 

 the temperature was least, as in the polar sea. As regards the 

 percentage of oxygen present at ditferent depths it diminishes 

 from the surface to a depth of 300 fathoms and increases from 

 that point to lower depths. Prof. Tait communicated two 

 laboratory notes ; (l) Two plates either of the same or different 

 metals were placed very close to one another but insulated and 

 one of them raised in temperature : a difference of potential was 

 produced, which was capable of producing a current mea- 

 surable by a sensitive galvanometer. (2) He had seen in 

 Dr. Blair's ** Scientific Aphorisms " a hypothesis to account for 

 gravitation very like that of Lesage's ultramundane corpuscles, 

 which Blair stated was suggested to him by Newton's works, 

 and Prof. Tait was anxious to ascertain if any part of it was due 

 to Lesage or was entirely original. Prof. Tait laid on the table 

 an algebraic identity which could be used to sum various series. 



Dublin 

 Royal Society, May 21.— Prof. J. Emerson Reynolds, 

 M.D. , in the chair. — The following papers were read : — On 

 some measurements of the polarisation of light coming from the 

 moon and from the planet Venus, by Earl Rosse, F. R. S. 

 Lord Rosse gave the results at which he had already arrived from 

 a very large number of observations on the polarisation of light 

 from particular parts of the moon's surface made in the years 

 1S72, 1S73, 1874, and 1S75, and which are still in progress. 

 The observations indtcate that the polarisation of the light 

 conring from the plains is greater than that of the light coming 

 from the mountainous regions. — Notes on the Crustacea of 

 Ireland, by Mr. William Andrews. An account of the rarer 



