present prevents the fire from spreading, a drop placed upon a piece of wood leaving after combustion only a charred spot. When not in use, the prisms should be kept in an iron pot with a tight cover. In this manner I have employed and preserved two during a long and hot summer. The viscid or, rather oily nature of the solution serves to prevent, to a great extent, the formation of ascending and descending currents from slight changes of temperature; and when the prisms are well shaken before use, the definition remains perfect for a long time. In my spectroscope the prisms rest upon a plate of glass instead of upon one of metal.—Silliman's American Journal, July 1870. ON THE PROPAGATION OF SOUND IN TUBES. BY M. AD. SEEBECK. It is admitted that the velocity of sound propagated in a tube is less than in the open air, and the smaller the tube the less the velocity*. Kirchhoff has given the following formula for the velocity of sound : in which A is the velocity in air, r the radius of the tube, n the number of vibrations, K a constant dependent on the calorific conductivity and on friction. This formula is the same as the one given by Helmholtz, except the meaning of the constant K. The method employed by Seebeck does not differ materially from that which Schneebeli adopted in order to verify Helmholtz's formula, and of which he has already given an account†. The apparatus used was constructed of a horizontal tube, closed near one end by a moveable piston; near the other a very narrow lateral tube was soldered, to which a caoutchouc tube was fitted which communicated with the ear. A sound was produced in front of the opening of the tube by means of a tuning-fork fixed horizontally to a piece of wood insulated by some caoutchouc supports. That the ear may hear distinctly the sound produced by the tuning-fork, at the junction of the large tube closed by the piston and the small tube communicating with the ear there must be a node, due to the coexistence of direct and reflected waves against the piston. If a loop is produced, the sound perceived by the ear will have its minimum intensity; it is this character which is to be appreciated; and it is then known whether the distance from the piston to the opening of the small tube is equal to, or in general to (2n+1), λ being the wave-length of the sound produced; from this we get the velocity of sound by the formula V-nλ, n being the number of vibrations of the corresponding sound. The whole section of the tube was agitated, which Kirchhoff's formula presupposes, except for the largest * Annales de Chimie et de Physique, S. 4. vol. xv. pp. 487, 492. † Ibid. vol. xvii. p. 512. tubes used. The observations were reduced to zero by means of the λι formula λ= by observing at the commencement and the √1+at end of each series of observations a thermometer placed close at hand the air in the tube was first dried by chloride of calcium. Seebeck used König's four tuning-forks, which give the notes ut, sol, mi, ut,, of which the numbers of vibrations were 512, 384, 320, 256. He found the following results:— The velocity of the sound diminishes with the diameter of the tube, except for the largest (2r= 29 millims.), which Seebeck attributes to the whole of the section not having been agitated; it may also be that in the large tubes the motion of the gaseous molecules is not parallel to their axis. By adopting for the velocity of sound in air a the number 332.77 millims., a result obtained from the determinations by Moll and Van Beek, Seebeck has calculated the difference A-V. According to the formula by Kirchhoff, we must have and consequently, for the same sound and various tubes, (A—V1) × 2r1 =(A—V2) × 2r2, an equation which the determinations of Seebeck satisfy, except for the largest tube (2r=29 millims.). But it was also found that (A-V)√n, for the same value of r, is no longer constant. Seebeck recognized, on the contrary, that the product (A-V)n was ob viously constant; and consequently the diminution of velocity of sound in a tube varies in inverse ratio with the power of the num ber of vibrations of the corresponding sound. Seebeck also made some investigations when the interior of his tubes was covered with leather or flannel: he proved that there was a considerable diminution in the velocity of sound; in the latter case it fell to 281.7 millims. These experiments, however, leave something to be desired, because the interior of the tube was not completely covered. A small slit was made that the position of the piston might be observed: would it not be possible to determine the position of the piston exactly by means of the rod by which it is regulated?-Poggendorff's Annalen, vol. cxxxix. p. 104; Annales de Chimie, April 1870. 1 Lectures on Mineralogy applied to Geology and the Arts are given by Professor TENNANT, F.G.S., at King's College, London, on Wednesday and Friday Mornings, from 9 to 10 o'clock, and on Thursday Evenings from 8 to 9, from October to Christmas, to which the public are admitted on paying the College Fees, namely, Two Guineas to the Morning Course, and One Guinea to the Evening. The Course commences with a description of the Physical and Chemical characters of Minerals in general, and includes a minute description of all the substances entering into the composition of Rocks, and of those Minerals which are also used in the Arts; illustrated by an extensive collection of characteristic specimens, and diagrams of the principal crystalline forms, &c. The Students are accompanied by the Professor to the Museum of Practical Geology, the British Museum, and other public institutions, and also on excursions into the country. MR. TENNANT also gives private instruction in Mineralogy and Geology at his residence, 149 Strand, London, W.C. TO GEOLOGISTS. Professor TENNANT has received instructions to dispose of, by private contract, the extensive and valuable Collection of Tertiary and other Fossils the property of N. T. WETHERELL, Esq., F.G.S., of Highgate. This Collection (well known as the North London) consists principally of a very large series of London-Clay Fossils and Minerals from Highgate and its vicinity, as also from Bognor, Bracklesham Bay, Hampshire, and Sheppey. The fossils are for the most part carefully arranged and named. Many of the specimens are the originals which have been figured in various works, while others are quite new to science. In addition to the above-named, there is an extensive series of Fossils and Minerals from the Boulder Clay of Muswell Hill and Finchley. Also numerous Fossils from the Chalk, the Greensand, Oolite, Lias, &c. Apply to Professor TENNANT, 149 Strand, London, W.C. MR. TENNANT, 149 Strand, London, W.C., has for sale two Cabinets, measuring 9 feet 3 inches long, 2 feet 4 inches wide, and 3 feet 10 inches high; each containing 45 drawers, with a Glass Case on the top of each Cabinet, 4 feet 11 inches high, and 15 inches from back to front. One Cabinet is filled with 2600 Minerals, the other with 3400 Fossils. The Collection consists of six thousand specimens, many very select. The first Gold Nugget received from Australia, which was exhibited in the Exhibition of 1851, is in the Collection; it cost £37, and contains about 8 ounces of gold: also a fine series of Diamonds, illustrating crystalline form and colour. The specimens have been used to illustrate the Lectures on Mineralogy and Geology at King's College, London, and at the Royal Military Academy, Woolwich. Price THREE THOUSAND GUINEAS. Any person wishing to become practically acquainted with the interesting and important study of Mineralogy and Geology will find this a good opportunity to obtain an instructive and valuable Museum, the specimens having been collected with care and at great expense during the last thirty years. Elementary Collections at 2, 5, 10, 20, 50, to 100 guineas each, and every requisite to assist those commencing the study of these interesting branches of Science, a knowledge of which affords so much pleasure to the traveller in all parts of the world. A collection for Five Guineas, to illustrate the recent works on Geology, by Ansted, Buckland, Lyell, Mantell, Murchison, Page, Phillips, and others, contains 200 specimens, in a plain Mahogany Cabinet, with five trays, comprising the following specimens. viz. :— MINERALS which are either the components of Rocks, or occasionally imbedded in them-Quartz, Agate, Chalcedony, Jasper, Garnet, Zeolite, Hornblende, Augite, Asbestos, Felspar, Mica, Talc, Tourmaline, Calcite, Fluor, Selenite, Baryta, Strontia, Salt, Sulphur, Plumbago, Bitumen, &c. NATIVE METALS, or METALLIFEROUS MINERALS; these are found in masses or beds, in veins, and occasionally in the beds of rivers. Specimens of the following Metallic Ores are put in the Cabinet:-Iron, Manganese, Lead, Tin, Zinc, Copper, Antimony, Silver, Gold, Platina, &c. Rocks: Granite, Gneiss, Mica-slate, Clay-slate, Porphyry, Serpentine, Sandstones, Limestones, Basalt, Lavas, &c. PALEOZOIC FOSSILS from the Cambrian, Silurian, Devonian, Carboniferous, and Permian Rocks. SECONDARY FOSSILS from the Rhætic, Lias, Oolite, Wealden, and Cretaceous Groups. TERTIARY FOSSILS from the Plastic Clay, London Clay, Crag, &c. In the more expensive collections some of the specimens are rare, and all more select. JAMES TENNANT, Mineralogist (by appointment) to Her Majesty, 149 Strand, London, W.C. September 1870. XIX. On the Cause of the Motion of Glaciers. By JAMES CROLL, of the Geological Survey of Scotland....... ... page 153 XX. On the Molecular Movements and Magnetic Changes in Iron &c. at different Temperatures. By G. GORE, F.R.S. XXI. On the Measurement of Wave-lengths by means of Indices of Refraction. By WOLCOTT GIBBS, M.D., Rumford Professor in Harvard University ... XXII. On the Probable Character of Cometary Orbits. By A. S. DAVIS, B.A., Mathematical Master, Leeds Grammar School...... XXIII. Experiments and Observations on the Adhesion between Solids and Liquids. By GIOVANNI LUVINI, Professor of Physics in the Royal Military Academy of Turin .... XXIV. Memoir on Internal Work in Gases. By M. ACHILLE XXV. Remarks on a Paper by Dr. Sondhauss " On the Tones of XXVII. Proceedings of Learned Societies: .... 170 177 183 190 197 211 218 ROYAL SOCIETY :-Mr. C. TOMLINSON on Supersaturated Saline 221 GEOLOGICAL SOCIETY:-Mr. W. CARRUTHERS on the Structure ..... : 225-227 On the Extension of Ohm's Laws to Electrolytes, and on the Nu- 227 On Liquids of High Dispersive Power, by Wolcott Gibbs, M.D., 229 On the Propagation of Sound in Tubes, by M. Ad. Seebeck 231 .. *It is requested that all Communications for this Work may be addressed, post-paid, to the Care of Messrs. Taylor and Francis, Printing Office, Red Lion Court, Fleet Street, London. Published the First Day of every Month.-Price 2s. 6d. THE LONDON, EDINBURGH, AND DUBLIN PHILOSOPHICAL MAGAZINE, AND JOURNAL OF SCIENCE. Being a Continuation of Tilloch's Philosophical Magazine,' CONDUCTED BY SIR ROBERT KANE, LL.D. F.R.S. M.R.I.A. F.C.S. AND WILLIAM FRANCIS, PH.D. F.L.S. F.R.A.S. F.C.S. FOURTH SERIES. N° 267.-OCTOBER 1870. WITH A PLATE, Illustrative of M. S. MERZ's Paper on an Object-glass Spectral apparatus. LONDON: PRINTED BY TAYLOR AND FRANCIS, RED LION COURT, FLEET STREET, Printers and Publishers to the University of London. Sold by Longmans, Green, Reader and Dyer; Kent and Co.; Simpkin, Marshall and |