difficulties are greatly reduced. If we superpose a layer of water upon a surface of mercury, the flatness and parallelism of the surfaces take care of themselves. The objection that the two surfaces would reflect very unequally may be obviated by the addition of so much dissolved colouring matter, e.g. soluble aniline blue, to the water as shall equalise the intensities of the two reflected lights. If the adjustments are properly made, the whole field, with the exception of a margin near the sides of the containing vessel, may be brought to one degree of brightness, being in fact all included within a fraction of a band. The width of the margin, within which rings appear, is about one inch, in agreement with calculation founded upon the known values of the capillary constants. During the establishment of equilibrium after a disturbance, bands are seen due to variable thickness, and when the layer is thin, persist for a considerable time. When the thickness of the layer is increased beyond a certain point, the difficulty above discussed, depending upon obliquity, becomes excessive, and it is advisable to change the manner of observation to that adopted by Michelson. In this case the eye is focused, not, as before, upon the operative surfaces, but upon the flame, or rather upon its image at E (Fig. 2). For this purpose it is only necessary to introduce an eye-piece of low power, which with the lens C (in its second operation) may be regarded as a telescope. The bands now seen depend entirely upon obliquity according to the formula above written, and therefore take the form of circular arcs. Since the thickness of the layer is absolutely constant, there is nothing to interfere with the perfection of the bands except want of homogeneity in the light. But, as Fizeau found many years ago, the latter difficulty soon becomes serious. At a very moderate thickness it becomes necessary to reduce the supply of soda, and even with a very feeble flame a limit is soon reached. When the thickness was pushed as far as possible, the retardation, calculated from the volume of liquid and the diameter of the vessel, was found to be 50,000 wave-lengths, almost exactly the limit fixed by Fizeau. To carry the experiment further requires still more homogeneous sources of light. It is well known that Michelson has recently observed interference with retardations previously unheard of, and with the aid of an instrument of ingenious construction has obtained most interesting information with respect to the structure of various spectral lines. A curious observation respecting the action of hydrofluoric acid upon polished glass surfaces was mentioned in conclusion. After the operation of the acid the surfaces appear to be covered with fine scratches, in a manner which at first suggested the idea that the glass had been left in a specially tender condition, and had become scratched during the subsequent wiping. But it soon appeared that the effect was a development of scratches previously existent in a latent state. Thus parallel lines ruled with a knife edge, at first invisible even in a favourable light, became conspicuous after treatment with acid. Perhaps the simplest way of regarding the matter is to consider the case of a furrow with perpendicular sides and a flat bottom. If the acid may be supposed to eat in equally in all directions, the effect will be to broaden the furrow, while the depth remains unaltered. It is possible that this method might be employed with advantage to intensify (if a photographic term may be permitted) gratings ruled upon glass for the formation of spectra. GENERAL MONTHLY MEETING, Monday, April 10, 1893. SIR JAMES CRICHTON-BROWNE, M.D. LL.D. F.R.S. Treasurer and Vice-President, in the Chair. W. H. Broadbent, M.D. Henry C. J. Bunbury, Esq. William Flockhart, Esq. Francis Gaskell, Esq. George W. Hemming, Esq. Q.C. Colin Charles Hood, Esq. Mrs. W. Rathbone, Granville R. Ryder, Esq. Mrs. Sharpe, F. W. Watkin, Esq. M.A. F.R.A.S. were elected Members of the Royal Institution. The special thanks of the Members were returned for the following Donation to the Fund for the Promotion of Experimental Research at low temperatures: Alexander Siemens, Esq. £21 The PRESENTS received since the last Meeting were laid on the table, and the thanks of the Members returned for the same, viz. :— FROM The Secretary of State for India-Archæological Survey of India, New Series, Vol. I. 4to. 1889. Report on Public Instruction in Bengal, 1891-2. fol. 1892. The Lords of the Admiralty-Nautical Almanac Circular, No. 14. 8vo. 1893. Accademia dei Lincei, Reale, Roma-Atti, Serie Quinta: Rendiconti. Classe di Scienze fisiche matematiche e naturali. 1o Semestre, Vol. II. Fasc. 3-5. 8vo. 1893. Rendiconti, Serie Quinta, Classe di Scienze Morali, Storiche e Filologiche, Vol. II. Fasc. 1. 8vo. 1893. Agricultural Society of England, Royal-Journal, Third Series, Vol. II. Part 1. 8vo. 1893. American Association for Advancement of Science-Proceedings, 41st Meeting, Rochester. 8vo. 1892. Astronomical Society, Royal-Monthly Notices, Vol. LIII. No. 4. 8vo. 1893. Bankers, Institute of Journal, Vol. XIV. Part 3 8vo. 1893. Birmingham Philosophical Society-Proceedings, Vol. VIII. Part 1. 8vo. 1891-2. British Architects, Royal Institute of-Proceedings, 1892-3, Nos. 11, 12. 4to. British Association for Advancement of Science-Report of Meeting at Edinburgh, 1892. 8vo. British Astronomical Association-Journal, Vols. I. II. III. No. 4. 8vo. 1890-3. Canada Geological and Natural History, Survey of-Contributions to Canadian Paleontology, Vol. I. Part 4. 8vo. 1892. Carpenter, H. S. Esq. (the Editor)-Bourne's Handy Assurance Manual. 8vo. 1893. Chemical Industry, Society of―Journal, Vol. XII. No. 2. 8vo. 1893. Civil Engineers, Institution of-Minutes of the Proceedings, Vol. CXI. 8vo. 1893. Dax, Société de Borda-Bulletin, Dix-septième Année, 3-4 Trimestre. Svo. 1892. Editors-American Journal of Science for March, 1893. 8vo. Analyst for March, 1893. 8vo. Athenæum for March, 1893. 4to. Author for March, 1893. Chemical News for March, 1893. 4to. Chemist and Druggist for March, 1893. 8vo. Electrical Engineer for March, 1893. fol. Electric Plant for March, 1893. Engineer for March, 1893. fol. 8vo. Engineering for March, 1893. fol. Horological Journal for March, 1893. 8vo. Iron for March, 1893. 4to. Ironmongery for March, 1893. 4to. 8vo. Nature for March, 1893. 4to. Open Court for March, 1893. 4to. Photographic Work for March, 1893. 8vo. Surveyor for March, 1893. 8vo. Telegraphic Journal for March, 1893. fol. Transport for March, 1893. fol. Zoophilist for March, 1893. 4to. East India Association-Journal, Vol. XXV. No. 1. 8vo. 1893. Electrical Engineers, Institution of-Journal, No. 104. 8vo. 1893. Florence Biblioteca Nazionale Centrale-Bolletino, Nos. 173, 174. 8vo. 1893. Franklin Institute-Journal, No. 807. 8vo. 1893. Geographical Society, Royal-Geographical Journal, Vol. I. No. 4. 8vo. 1893. Institute of Brewing-Transactions, Vol. VI. No. 5. 8vo. 1893. Johns Hopkins University-American Chemical Journal, Vol. XV. No. 2. 8vo. 1893. Studies in Historical and Political Science, Eleventh Series, No. 2. 8vo. 1893-4. University Circular, No. 103. 4to. 1893. Junior Engineering Society-Record of Transactions, Vol. II. 8vo. 1891-2. Manchester Geological Society-Transactions, Vol. XXII. Parts 3, 4. 8vo. 1893. Manchester Literary and Philosophical Society-Memoirs and Proceedings, Vol. VII. No. 1. 8vo. 1892-3. Massachusetts Institute of Technology, Boston, U.S.A.-Technological Quarterly, Vol. V. No. 3. 8vo. 1892. Meteorological Society, Royal-Quarterly Journal, No. 85. 8vo. 1893. Montpellier, Académie des Sciences et Lettres-Mémoires, Tome XI. Fasc. 3. 4to. 1892. Payne, Wm. W. Esq. and Hale, Geo. E. Esq. (the Editors)—Astronomy and Astro- Pharmaceutical Society of Great Britain-Journal for March, 1893. 8vo. Preussische Akademie der Wissenschaften-Sitzungsberichte, Nos. XLI.-LV. 8vo. 1892. Prince, C. Leeson, Esq. F.R.A.S. (the Author)—The Summary of a Meteorological Journal for 1892. Richards, Admiral Sir G. H. K.C.B. F.R.S. (the Conservator)-Report on the Navigation of the River Mersey, 1892. 8vo. 1893. Rio de Janeiro, Observatoire Impérial de-Annuario, Anno VIII. 8vo. 1892. Le Climat de Rio de Janeiro. By L. Cruls. 8vo. 1892. Royal Society of London-Proceedings, No. 319. 8vo. 1893. Saxon Society of Sciences, Royal-Mathematisch-physische Classe, Berichte, 1892, Nos. 4-6. 8vo. Sidgreaves, Rev. W. F.R.A.S. (the Author) - Spectrum of Nova Auriga. 4to. 1893. Société Archæologique du Midi de la France-Bulletin, No. 10. 8vo. 1892. Society of Arts-Journal for March, 1893. 8vo. Stannus, Hugh, Esq. F.R.I.B.A. (the Author)—The Theory of Storiation in Applied Art. 8vo. 1893. Tacchini, Professor P. Hon. M.R.I. (the Author)-Memorie della Societa degli Spettroscopisti, Italiani, Vol. XXII. Disp. 3. 4to. 1893. United Service Institution, Royal-Journal, No. 181. 8vo. 1893. United States Department of Agriculture-Monthly Weather Review for December, 1892. 4to. 1893. Vereins zur Beförderung des Gewerbfleisses in Preussen-Verhandlungen, 1893. Heft 2. 4to. 1893. WEEKLY EVENING MEETING, Friday, April 14, 1893. SIR FREDERICK ABEL, K.C.B. D.C.L. D.Sc. F.R.S. Vice-President, in the Chair. SIR WILLIAM H. FLOWER, K.C.B. D.C.L. LL.D. D.Sc. F.R.S. Seals. SIR WILLIAM FLOWER began by recalling that about two years ago Lord Salisbury, while taking a comprehensive survey of the general state of international politics, remarked that there were, happily, then, no graver subjects to excite the anger and jealousy of rival nations than seals and lobsters, and it was to the study of the habits of these animals that the energies of diplomatists were mainly directed. In the present lecture it was proposed to speak only of seals, and, taking the common seal as a type, he described its general character and position in the Animal Kingdom. The lecturer then passed in review the distinctive traits and geographical distribution of the various allied species of true seals, and pointed out their economic uses and mode of capture. The next animal treated of was the walrus, and finally, the third group into which the seals are divided the eared-seals, sea-lions, or sea-bears. These differ from the true seals in possessing small external ears, and in the power of using their hind feet in walking on land like ordinary quadrupeds. It is animals of this group which yield the beautiful fur called "sealskin" in commerce, and the lecture was illustrated by specimens of this fur in various stages of preparation. The wholesale destruction of fur-seals which formerly went on throughout the southern hemisphere was next spoken of, and a more detailed account given of the very remarkable habits of the species from the Behring Sea, which for many years has been the main source of supply of sealskin dresses, and the right of capture of which is now the subject of controversy between Great Britain and the United States. After giving an outline of the questions, as far as they related to the natural history of the animals, to be placed before the arbitrators, he concluded by saying that we can scarcely be too grateful to the statesmen of both nations for having so far agreed as to bring the whole of this difficult and complicated question before such a tribunal as that now sitting at Paris. VOL. XIV. (No. 87.) [W. H. F.] G |