The Chair was then taken by Prof. Prestwich, M.A., F.R.S., Vice-President. 3. "On Pelanechinus, a new Genus of Sea-urchin from the Coral Rag." By W. Keeping, Esq., B.A. F.G.S., Professor of Geology in the University College of Wales. 4. "Remarks on Saurocephalus, and on the Species which have been referred to that Genus." By E. Tulley Newton, Esq., F.G.S., of H.M. Geological Survey. 5. "A Microscopical Study of some Huronian Clay-slates." By Dr. Arthur Wichmann. Although a considerable amount of attention has been devoted during recent years to the microscopical study of clay-slates and slate-clays, yet in none of the published researches on this subject has any account of the structure of the clay-slates of archæan age been given. The author has availed himself of the extensive series of Huronian clay-slates collected by Major T. V. Brooks in the country around Lake Superior to supply this deficiency. The succession and relation of the rocks described have been fully treated of in the work of Hermann Credner and the publications of the Geological Survey of Michigan. The chief object of the author is to discuss the origin of the crystalline constituents in clay-slates, and at the outset he describes in detail the microscopical character of clay-slate, of novaculite or whetstone, and of carbonaceous shales and slates respectively, dwelling more especially on the crystallized minerals which can be detected in each of these rocks, and the nature of the isotropic ground-mass which sometimes surrounds them. He then points out that three theories have been advanced to account for the presence of these crystalline constituents in clay-slates. According to the first of these theories, the crystals in question are regarded as the product of chemical action in the ocean in which the original material was deposited; the second theory attributes the formation of the crystalline minerals to processes of metamorphism which have taken place subsequently to the solidification of the rocks ; the third theory refers them to aggregative action going on in the still plastic clay-slate mud prior to its solidification. The first of these theories has been maintained by G. R. Credner; but against it the author adduces numerous arguments, and especially points out the difficulty of supposing an ocean capable of depositing from its waters at successive periods minerals of such different chemical composition as chlorite, actinolite, &c. In opposition to the second theory, which has received the support of Delesse, the author points out the existence in the rocks in question of broken crystals which have been recemented by the surrounding clay-slate substance. The author is thus led to incline towards the third theory, in favour of which some striking facts, drawn from the microscopical structure of the rocks, have already been adduced by Zirkel. He admits, however, that later metamorphic actions are not to be excluded in seeking to account for the origin of the crystalline constituents of clay-slates, and points out that four distinct stages must be considered in the series of changes by which the rocks in question have acquired their present character:-1st, the deposition of the mud; 2nd, the formation of minerals during the plastic state; 3rd, the separation of materials during solidification; and 4th, the action of metamorphic processes. 6. "On a Section through Glazebrook Moss, Lancashire." By T. Mellard Reade, Esq., F.G.S. The section described has been exposed in a cutting made by the Wigan Junction Railway. The moss rests on an almost perfectly level floor of Boulder-clay, and is at the deepest part about 18 feet thick. In the 3 or 4 feet at the base are branches &c. of trees; and the stools are found resting on and rooted in the Boulder-clay; these are of oak or birch. Prostrate trunks were found, one, an oak, being 46 feet long and 3 in diameter. The surface of the clay is about 60 feet above O.D. The author thinks the section shows that the moss originated from the decay of the forest, favoured by change of climate, and gradually extended itself from the centre outwards, trees within it at the outer part being much less discoloured than those further in. In the latter part of the paper some cuttings and borings in the clays and sands are described, and the asserted occurrence of the trunk of a tree in the Boulder-clay is noticed. 7. "On the Tertiary Deposits on the Solimões and Javary Rivers in Brazil." By C. B. Brown, Esq. With an Appendix by R. Etheridge, Esq., F.R.S., F.G.S., and communicated by him. The author in 1874 had the opportunity of examining some beds on the Solimões, or Upper Amazon, and the Javary, one of its tributaries, containing fresh- and brackish-water shells similar to those found in Tertiary deposits at Pebas, still higher up the river. The author indicates certain errors into which he considers previous writers to have fallen, and calls attention to the great extent of these beds, now demonstrated to occupy a tract of country 300 miles in length by 50 miles in breadth, and to the enormous change in the physical features of the region which must have taken place since their deposition. When this took place the sea reached probably 1500 miles west of its present shore-line, covering the country which is now the valley of the Amazon. The absence of examples of false-bedding in the deposits leads him to the conclusion that they were formed in comparatively still water, into which flowed numerous streams bearing much vegetable matter, which has served for the formation of lignitic deposits, the whole being probably the upper beds of a series deposited under similar conditions to those of deltas in the present day. In an appendix, Mr. Etheridge notices the fossils collected by the author, which included seeds of Chara, and species of Mytilus (1 new), Anisothyris (4, 1 new), Lutraria (1), Thracia (1), Anodon (1), Unio (1), Natica? (1), Neritina (2 new), Odostomia (1), Hydrobia (1 new), Isaa (1), Dyris (1), Assiminea (1 new), Fenella (1), Cerithium (2 new), Melania 4( new), and a new Gasteropod constituting a genus (Alycæodonta) allied to Alycæus. A single palatal plate of Myliobatis or Zygobatis (probably derived) was also found. 8. "On the Physical History of the English Lake-district, with Notes on the possible Subdivision of the Skiddaw Slates." By J. Clifton Ward, Esq., Assoc.R.S.M., F.G.S. The author traces the physical history of the lake-district from the commencement of the period when the Skiddaw slate was deposited. To this succeeded the volcanic Borrowdale series, which is followed after a physical break by the Coniston Limestone. Between this and the succeeding Silurian deposits there is little, if any, break. Thus, in the Lake-district, the break between Upper and Lower Silurian is physically below the Coniston Limestone, though palæontologically it is above it. The Old Red Sandstone period was one of denudation, which was continued into the Carboniferous period; and perhaps the whole district was actually covered by the sea during the maximum depression of the Lower Carboniferous epoch. Since then it has probably never been submerged, but exposed to continuous subaerial denudation. The physical significance of the Mell-Fell (Lower Carboniferous) conglomerates receives special attention. The author then, from consideration of the amount of deposition and rate of denudation, attempts to estimate the period which has elapsed since the commencement of the record, and sets it down as 62,000,000 of years. The author then considers the age of the Skiddaw slates. From lithological resemblances he is led to correlate the Skiddaw grit with the basement grit in the Welsh Arenig series, and thus to regard the beds below the grit as the equivalent of the Tremadoc, and perhaps of part of the Lingula Flags. The paleontological evidence for the correspondence of the Arenig series with the whole of the Skiddaw slates rests chiefly on Graptolites and Trilobites. The author holds that the evidence from the former is inconclusive, and that from the latter to some extent contradictory, so that the physical evidence can in no way be overridden by it. 9. "On some well-defined Life-zones in the Lower Part of the Silurian (Sedgw.) of the Lake-district." By J. E. Marr, Esq. 10. "On the Upper Part of the Bala Beds and Base of Silurian in North Wales." By F. Ruddy, Esq. Communicated by Prof. T. M'K. Hughes, M.A., F.G.S. The author describes a series of sections in the upper part of the Bala and the succeeding beds, and gives lists of fossils. Details of the various beds between the Bala and Hirnant Limestone are given, above which come soft blue shales underlying Tarannon shales, when fossils cease until the base of the Wenlock is reached. The author has been able to trace the Hirnant Limestone and grit considerably beyond the limits of the Hirnant valley. The sections at Cynwyd (to the west of Corwen) are described. Here occur the equivalents of the Bala Limestone and beds above this up to the level (probably) of the Hirnant Grit. XLIII. Intelligence and Miscellaneous Articles. A SPECTROMETRIC STUDY OF SOME SOURCES OF LIGHT. BY A. CROVA. THE HE general law of emission of the radiations emitted by a body raised to an elevated temperature is not completely known. Dulong and Petit* have given the empirical law of the obscure radiations emanating from a body heated to temperatures below 240°; and Edm. Becquerelt has demonstrated that the intensity of the red, green, and blue radiations varies with the temperature of the body which emits them, according to an exponential law analogous to that of Dulong and Petit. The exponentials which represent the law of emission of radiations of different refrangibilities are represented by curves of which the origin corresponds to the temperature at which the radiation considered commences to be produced, and rises the more rapidly as the wave-lengths of the radiations become less. According to M. Edm. Becquerel, the logarithms of the bases of these exponentials vary in the inverse ratio of the wave-lengths of the radiations. These considerations may serve as a starting-point to a method of determination, in a spectrometric way, of the temperature of incandescent solids or liquids. In fact it follows from the investigations of Mr. Draper‡ and M. Edm. Becquerel that, when the temperature of an incandescent solid increases in a continuous manner, the spectrum of the radiations emitted by it lengthens towards the violet end, and that each of the radiations of this spectrum is at the same time increased in intensity according to an exponential formula. The temperature of the luminous source can therefore be measured :-(1) by means of the wave-length of the radiation which limits the spectrum towards the violet; (2) by the position of the thermal maximum of the spectrum, which approaches nearer to the violet in proportion as the emission-temperature becomes higher; (3) by means of the ratio of the luminous intensity of a determinate radiation λ, taken in the spectrum of the source, to the intensity of the same radiation in the spectrum of a source of known temperature, compared with the ratio of the luminous intensities of another radiation a' in the same two spectra. These last determinations can be easily effected by means of a spectrophotometer. Several observers have made use of instruments of this kind §. I used that of M. Glahn, which permits measurements to be made upon homogeneous radiations. On the other hand, I have measured the thermal intensity of the simple radiations of the solar spectrum by means of a linear thermoelectric pile and a very sensitive galvanometer, using for the * Ann. de Chimie et de Physique, 2e série, t. vii. + Edm. Becquerel, La Lumière, t. i. pp. 61-67. Phil. Mag. 1847, vol. xxx. p. 345. $ Govi, Comptes Rendus, t. 1. p. 156 (1860). Trannin, Journal de Physique, t. v. p. 297. Vierordt, Pogg. Ann. 5th series, vol. xx. Glahn, Wiedemann's Annalen, vol. i. (1877). first trials a flint-glass prism and a glass concave mirror silvered at its surface instead of an achromatic lens. The employment of a network of lines engraved on the metal instead of the prism would permit the influence of any elective absorption to be eliminated. I have made numerous determinations of thermal curves of the solar spectrum on exceptionally fine days, at different periods in the years 1877 and 1878. These curves differ in the ratio of their respective ordinates, but especially in the position of the thermal maximum, as has been shown by Melloni. These curves were rendered comparable with one another by bringing them to the scale of the wave-lengths, and reducing, by means of the dispersion-curve of the prism, the intensities to those which would correspond to the theoretic case of the normal spectrum-that is, of constant dispersion. The following are, for the luminous part of these spectra, the means of a number of concordant observations made under excellent atmospheric conditions: millim. millim. millim. millim. millim. millim. 0.000676 0.000605 0·000560 0·000523 0-000486 0·000459 1000 820 760 670 540 460 I have represented by 1000 the thermal intensity which corresponds to a red radiation of wave-length 0.000676 millim.; the intensities measured in the ultra-red cannot find a place in this Table, the corresponding wave-lengths not being accurately known. Now here are the ratios of the luminous intensities of the same radiations of the spectra of the following sources, compared with the light of the sun : Wave-lengths millim. millim. millim. millim. millim. millim. 0.000676 0.000605 0·000560 0·000523 0.000486 0.000459 777777 The electric light was from 60 large Bunsen elements, Foucault regulator, with M. Carré's carbons in the focus of a metallic concave mirror; the Drummond light, oxygen and illuminating-gas thrown upon lime; the moderator lamp, fed with colza-oil. I measured the ratio of the intensity of each of the radiations of these spectra, corresponding to the wave-lengths of the preceding Table, to the intensity of the same radiation in the solar spectrum, representing these latter by the value of their thermal intensities, and always representing by 1000 the intensity corresponding to the wave-length 676. For luminous radiations which have undergone no weakening by previous transmission, there would be proportionality between the thermal and luminous intensities of one and the same radiation, whatever its origin, as MM. Jamin and Masson have demonstrated; but the experiments of M. Desains* have shown that, in the con*Comptes Rendus, t. lxvii. p. 297. |