286 



NA TURE 



[January i8, 1900 



described may be explained as the effects of earth-movement on 

 a group of rocks consisting of limestone passing up into tuff, 

 interbedded with lava-flows, and possibly traversed by sills or 

 dykes of basaltic rock. The results of the disturbance appear 

 to be limited vertically and horizontally, and to have been deter- 

 mined by the differential resistance of the component rocks. 

 Analogous features occur in the Borrowdale volcanic series and 

 in the Silurian volcanic rocks of Portraine. The President, 

 after congratulating the author on his paper, read the following 

 extract from a letter that he had received from Sir Archibald 

 Geikie, who was unable to be present :— " Having been twice 

 with Mr. Lamplugh over the ground which he describes, the 

 second time quite recently, since his present views as to earth- 

 movement were formed and matured, I am glad to bear my testi- 

 mony to the exhaustive care which he has expended on the 

 research. I agree with him on the main point— that there is 

 conclusive evidence of considerable earth-movement since the de- 

 position of the Carboniferous volcanic rocks at the southern end 

 of the Isle of Man. He seems to me to have established this point 

 beyond dispute." — The zonal classification of the Wenlock 

 shales of the Welsh borderland, by Miss Gertrude L. EUes. 

 This paper deals with the Wenlock rocks of Builth, the Long 

 Mountain, and the Dee Valley. The results obtained by the 

 author completely confirm the work of Tullberg on the Wenlock 

 shales of Southern Sweden. In the discussion which followed. 

 Prof. C. Lapworth pointed out the extreme interest of this paper, 

 both from the stratigraphical and from the palseontological point 

 of view. The zonal mapping of the Welsh Silurians com- 

 menced by Prof. Watts, carried through the Rhayader Valentian 

 by Mr. Herbert Lapworth, had here been brought out in detail 

 stage by stage through the Wenlocks of the Welsh border by the 

 author. — On an intrusion of diabase into Permo-Carboniferous 

 rooks at Frederick Henry Bay (Tasmania), by T. Stephens. The 

 relationship of the abundant diabase to the Permo-Carboniferous 

 strata of the island has been long a matter of dispute. Among 

 others,Jukes describes sections which appeared to confirm the view 

 that Permo-Carboniferous sediments were deposited round vast 

 masses of igneous rock previously cooled and denuded. The 

 author has identified and visited the sections, and finds in one 

 that, although there is a step-like junction between the sedi- 

 ments and the igneous rock, it is the result of the intrusion of 

 diabase, and not of the deposition of sediment. The sediment, 

 which is fossiliferous, is converted into an intensely hard whitish 

 marble, and the associated shale-bands into chert. The diabase, 

 which is ordinarily an ophitic rock, acquires at the junction a 

 finely crystalline-granular texture. Jukes's second section also 

 gives undoubted evidence of intrusion. 



Mathematical Society, January ii. — Lieut. -Colonel 

 Cunningham, R.E., Vice-President, in the chair. — Prof. Love, 

 F.R.S., communicated a paper, by Mr. J. H. Michell, on ele- 

 mentary distributions of plane stress. — Lieut. -Colonel Cunning- 

 ham (Mr. Kempe, F.R.S., pro tern, in the chair) gave a 

 preliminary sketch of a general method of factorisation of 

 biquadratics, with special application to quartans, N = x*-t-jj/*. — 

 The following abstract of a paper by Prof. H.Lamb, F. R.S., 

 entitled " A Problem in Resonance, illustrative of the Mechanical 

 Theory of Selective Absorption of Light," was read by Mr. 

 Tucker. — The impact of sound- waves on a fixed spherical obstacle 

 was discussed by Lord Rayleigh in a well-known paper {Proc. 

 Lond. Math. Soc, vol. iv. p. 253, 1872), which also treats briefly 

 the case where the sphere is movable, but is urged towards a 

 fixed position by a force varying as the displacement (/.c. p. 272). 

 In the present paper this latter problem is studied under a more 

 general form, it being supposed that the sphere is capable of 

 various independent modes of free vibration ; and special atten- 

 tion is directed to the case where there is coincidence, or 

 approximate coincidence, between the period of the incident 

 waves and that of one of the free modes. The immediate acoustical 

 importance of the question is perhaps not very great, since mas- 

 sive bodies are not usually set into vigorous sympathetic vibra- 

 tion by the direct impact of air-waves (the extreme precision 

 of tuning that would be required militates against this), but 

 rather through the intermediary of resonance-boxes and sounding 

 boards. The problem has, however, an interest in another 

 direction, as furnishing an analogy by which we can illustrate, 

 without any great expenditure of analysis, the mechanical theory 

 of selective absorption of light in a gas. — A paper by Dr. L. E. 

 Dickson, an abstract simple group of order 25920, was also 

 communicated. 



NO. 1577, VOL. 61] 



Manchester, 

 Literary and Philosophical Society, January 9. — Prof, 

 Osborne Reynolds, F. R.S., Vice-President, in the chair. Mr. 

 Thomas Thorp exhibited two film-gratings of a ruling designed 

 to weaken the image and to condense the illumination in the 

 spectra of the first and second order, and thus to compete with 

 the prism spectrum in brilliancy. — Geometrical representation 

 of the relation between wave-velocity and group-velocity, by 

 Prof. Horace Lamb, F.R.S. In any medium where the wave- 

 velocity varies with the wave-length, a simple geometrical 

 representation of the group-velocity is obtained by constructing 

 a curve with the former magnitude as ordinate and the latter as 

 abscissa. The group-velocity is then given by the length inter- 

 cepted by the tangent to the curve on the axis oiy. Thus, for 

 gravity waves on deep water the curve is a parabola, and it 

 appears at once that the group-velocity is one-half the wave- 

 velocity, as is well known. Various other cases are illustrated 

 in like manner ; in particular, the case when the waves are of 

 such moderate length that both gravity and surface-tension 

 have to be taken into account. The existence of a minimum 

 group-velocity, equal to 1.211 times the minimum wave-velocity, 

 is pointed out. 



Edinburgh. 



Royal Society, January 8. — Sir William Turner in the 

 chair.— Dr. W- Craig Maclagan read a paper on two historical 

 fallacies : Heather Beer and Uisge Beithe. After discussing 

 the various literary references and oral traditions concerning 

 heather beer, the author proceeded to describe his own attempts 

 to brew the so-called ale according to several detailed recipes. 

 In this he had the valuable assistance of Mr. Melvin, of the 

 Boroughloch Brewery, Edinburgh. All attempts to obtain from 

 heather a decoction capable of alcoholic fermentation failed 

 absolutely. The tradition seems to have had its source in the 

 idea that there must be sugar in the heather flower since bees visit 

 it ; but analysis proves that there is no real sugar present, but that 

 there is beeswax. A similar investigation proved that the 

 uisge beithe or birch ale had as fabulous an origin as heather 

 beer. — Sir John Murray communicated a paper by Mr. R. E. 

 Peake and himself on the Azores bank, and some recent deep- 

 sea soundings in the North Atlantic. From Mr. Peake's 

 soundings around the Azores, the configuration of the bottom 

 could now be shown in great detail. In depths less than 2000 

 fathoms the bottom was found to be very irregular, the bank 

 falling in some places from a depth of 1400 to 2400 fathoms 

 within a distance of five miles. Four new " deeps " or depths 

 exceeding 3000 fathoms had been discovered — the Peake Deep 

 between the Azores and the English Channel, and the Libbey, 

 Sigsbee and Thoulet Deeps to the south of the "tail" of the 

 banks of Newfoundland. Some remarkable differences in 

 bottom temperature had been observed ; for example, the tem- 

 peratures taken on the southerly of two lines between the 

 Azores and North America were about half a degree lower than 

 those taken on the northerly line ; and the temperatures along 

 the northerly of two lines between the Azores and the British 

 Isles were about three-quarters of a degree lower than the others. 

 —Dr. W. Peddie and Mr. A. B. Shand, in a paper on the 

 thermoelectric properties of solid and liquid mercury, described 

 how by the use of solid carbonic acid they had traced the 

 thermoelectric line of mercury well below its freezing-point. 

 The line seemed to be a fairly continuous straight line down to 

 the lowest temperature reached ; it lay nearly parallel to the 

 iron line, converging slightly so as to pass through a neutral point 

 about - 550° C. It cut the line of 0° C. a little below the copper 

 line. — A paper was also read on an optical method of deter- 

 mining the density of sea-water, by Mr. John J. Manley. The 

 apparatus used was the hollow quartz prism and spectrometer 

 belonging to the. Royal Society of London. Into this the 

 various samples of sea- water were put in succession, and the 

 deviations of t-he D line compared with the deviation due to 

 distilled water. All precautions were taken, and the method 

 was found to have several advantages as regards rapidity and 

 convenience over the usual methods of comparing densities of 

 sea-water. 



Mathematical Society, December 12, 1899.— -Mr. R, F. 

 Muirhead, President, in the chair. — Dr. Peddie gave an address 

 on the dissipation of energy in vibrating matter, with lime-light 

 illustrations.— It was agreed that Professor Gibson's paper on 

 Proportion be printed in the Society's Proceedings. 



