Vol. 40. No. 264. JULY 1870. 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° 264.-JULY 1870. CLONDON: 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 Now ready, in 12mo, price 3s. 6d. cloth, ALGEBRAICAL EXERCISES AND PROBLEMS WITH ELLIPTICAL SOLUTIONS, Framed so as to combine constant practice in the Simple Reasoning usually required in the Solution of Problems with constant practice in the Elementary Rules, the Simplification of Fractions and other Expressions, and in the Mechanical Operations of Algebra generally; with an Appendix containing Simple and General Methods, on one uniform plan, for resolving Algebraical Expressions into their Elementary Factors. By HUGH MCCOLL, Late Mathematical Master at the Collège Communal, Boulogne-sur-Mer. NEW WORKS BY PROFESSOR TYNDALL. Just published, in 8vo, with 6 Copper Plates and numerous Woodcuts, price 14s. cloth, RESEARCHES ON DIAMAGNETISM AND MAGNECRYSTALLIC ACTION: Including the Question of Diamagnetic Polarity. Professor of Natural Philosophy in the Royal Institution. By the same Author, also just published, in crown 8vo, price ls. sewed, or 1s. 6d. cloth, NOTES OF A COURSE OF NINE LECTURES ON LIGHT, Delivered at the Royal Institution of Great Britain in April-June 1869. London: Longmans, Green, and Co., Paternoster Row. THE QUARTERLY JOURNAL OF SCIENCE, Conducted by Sir W. FAIRBAIRN, Bart., F.R.S., W. CROOKES, F.R.S., R. HUNT, F.R.S., H. WOODWARD, F.G.S., and JAMES SAMUELSON, of the Middle Temple, Barrister-at-Law, Editor. No. XXVII. July 1870, with several Illustrations, price 5s.: I. Beer, Scientifically and Socially considered. Illustrated with Three Page Plates and Eight Woodcuts. By JAMES SAMUELSON, Editor. II. Spiritualism viewed by the Light of Modern Science. By WILLIAM CROOKES, F.R.S. III. The Rate of Geological Change. By H. M. JENKINS, F.G.S., Secretary to the Royal Agricultural Society of England. IV. Air-pollution by Chemical Works. V. De Mortuis. By HENRY WOODWARD, F.G.S., F.Z.S., &c. VI. Foreign Trees and Plants for English Gardens. With Woodcuts. BENNETT, M.A., B.Sc., F.G.S. VII. A Recent Triumph of Synthetical Chemistry. Reviews and Chronicles of Science. London: Longmans, Green, and Co., Paternoster Row. By ALFRED W. In crown 8vo, with 13 Illustrations (6 coloured), price 10s. 6d. The Plurality of Worlds studied under the Light of Recent Scientific Researches. "A most interesting work on a very fascinating subject."-Examiner. "In a book far more entertaining than any modern novel, Mr. Proctor has given us, amongst a number of other studies of worlds in physical conditions widely different from that of our own, a chapter of the highest interest on Mars, the miniature of our Earth."- Spectator. "A book treating learnedly, yet simply and intelligibly, of those great questions concerning the laws of the universe of which the outside world has lately heard so much and understood so little, and written in such excellent English that its literary merits are nearly equal to its scientific value. The work differs from most of its class in being full of original matter, which, though familiar to the astronomer, is quite new to the general reader."Scientific Opinion. "We can assure the reader that he will find in this volume the latest information, and much that is interesting and important. The views expressed as to the constitution of the sidereal universe, differ from those usually held, are clearly expressed, London: Longmans, Green, and supported by strong arguments and original and forcible evidence. Mr. Proctor has evidently considered this subject carefully. In the part of the book which relates to the solar system, useful information is more especially given to the nonscientific reader."-Athenæum. "A new work from Mr. Proctor's pen is hailed by all interested in the science of astronomy. Mr. Proctor's subject is most interesting, and he has produced a very readable book, which will prove attractive alike to scientific and non-scientific readers. Speculations as to the conditions under which beings like ourselves would exist if inhabiting the planets have often been brought forward; and Mr. Proctor has here treated the matter in the same careful and exhaustive manner which characterized his work on Saturn and its System.'. . . . We heartily recommend the perusal of this volume to every lover of the science of Astronomy. Unlike many scientific works, a tone of reverence towards the Creator of all things runs through the book, which is greatly to be commended."-Astronomical Register. and Co., Paternoster Row. [ADVERTISEMENTS continued on 3rd page of Cover. THE LONDON, EDINBURGH, AND DUBLIN PHILOSOPHICAL MAGAZINE AND JOURNAL OF SCIENCE. [FOURTH SERIES.] JULY 1870. I. On the Cause of the Descent of Glaciers. AFTER a long period of rest, the controversy respecting the motion of glaciers which occupied so much of the attention of scientific men during the period between 1842 and 1858 has been lately reopened. The Rev. Henry Moseley, who had already in 1855 proposed a theory which failed to obtain the adhesion of men conversant with the facts of glacier-motion, made a communication to the Royal Society in January 1869, wherein he sought to establish the insufficiency of the theory generally accepted by men of science. The mathematical investigation on which he grounded the results given in that paper was communicated to this Journal in May 1869. Having cleared the way by removing from his path the established theory, Canon Moseley proceeded to prepare for the admission of his own views by two papers which also appeared in this Journal. In August last he published an elaborate mathematical investigation of the problem of the "descent of a solid body on an inclined plane when subjected to alternations of temperature;" and this was followed in January last by a paper upon "The Mechanical Properties of Ice," embodying the results of observations and experiments made by himself and others upon the dilatation, tenacity, and shearing-force of ice. At a Meeting of the Bristol Naturalists' Society in December last, Canon Moseley gave a tolerably full exposition of his own theory, and has lately developed the same views, nearly in the same * Communicated by the Author. Phil. Mag. S. 4. Vol. 40. No. 264. July 1870. B terms, before a London audience, at the theatre of the Royal Institution. The arguments of Canon Moseley have not passed unquestioned. In March 1869 Mr. James Croll published in these pages a reply to Canon Moseley's paper shortly before communicated to the Royal Society, wherein, after admitting that the argument directed against the "ordinary opinion" on the subject of glacier-motion must be considered "decisive," he attempted to refute the general conclusion by ingenious considerations as to the condition of the molecules of a mass of ice when acted on by external heat. In the Alpine Journal' for February last, Mr. William Mathews, well known as a successful explorer of the Alps, and familiar with the phenomena of glaciers, has given an able summary of the present state of our knowledge of the causes of glacier-motion, along with a careful analysis of the views of Canon Moseley as developed in his various writings. In the same paper several weighty objections to Canon Moseley's views are urged by Mr. Mathews; and the result of an interesting experiment made by the writer, in conjunction with Mr. A. F. Osler, added a fact of considerable value to the materials available in the discussion. A further experiment, made by the same observers under circumstances that much enhanced its importance, was published by Mr. Mathews in the Number of 'Nature' for the 24th of March last. The latest contribution to the discussion with which I am acquainted is a reply by Canon Moseley to the strictures of Mr. Mathews, published in the 'Alpine Journal' for May 1870. 66 I trust that I shall be acquitted of any want of respect for the learned and ingenious author of what has been well termed the 'crawling theory" of glacier motion, if I discuss it very briefly,. and content myself with pointing out a few only of what appear to me insurmountable objections to its acceptance. It was sug gested, as is well known, by the casual observation of the gradual descent of sheet lead on a roof of moderate pitch. Although the resistance of friction was far greater than the force of gravity acting in the direction of descent, it was found that the lead continued to slide or crawl down the slope, and was even able to draw out nails that had been driven through it into the rafters beneath with a view to hold it fast. Mr. Moseley detected the physical cause of the phenomenon. He showed that it was a necessary consequence of alternations of temperature. When a body lying upon an inclined plane expands under the influence of heat, the expansion is mainly in the direction of least resistance. When acting in the upward direction, the expansive force has to overcome the resistance opposed by friction, and, in addi tion to this, that of the weight of the portion of the body driven up the slope. In the opposite direction, the weight of that portion which moves down the inclined plane acts along with the expansive force to overcome the resistance of friction. The inverse process occurs when the body contracts under the influence of cold; the larger portion of the mass will descend, and the smaller part only will ascend. Hence every alternation of temperature must cause a proportional, however slight, movement of the centre of gravity in a downward direction, and a corresponding descent of the whole mass. In order to deduce from this observation an explanation of the motion of glaciers, it was necessary to assume that a glacier lying in an alpine valley is a continuous solid, comparable in structure to the sheet of lead upon a roof, that under the influence of sunshine, shade, radiation, &c. its temperature is subject to frequent alternations, and, finally, that the consequence of such changes of temperature is to cause the entire mass of the glacier to expand and contract in the direction of its length. I have never met any one practically conversant with the phenomena of glaciers who could be brought seriously to discuss this theory, for the simple reason that every one of these assumptions is at variance with the facts of nature. So far from being a continuous solid mass like a sheet of metal, the ordinary condition of glacier-ice is that of a mass of more or less imperfectly welded separate portions, traversed by fissures, and whose upper surface is very frequently cut by deep rents extending to a depth very much greater than that subject to the influence of external changes of temperature. In the next place we have every possible ground, both from à priori reasoning and direct observation, for believing that the temperature of the interior of a glacier is very nearly constant, varying only by a small fraction of a degree from the freezingpoint. Professor Forbes long ago made the obvious objection that the temperature of ice cannot rise above 32° F., while, on the other hand, no cause has been suggested that can tend sensibly to lower the temperature of the interior below that limit. Every one familiar with glaciers is aware that nothing is so rare as to find the surface of a glacier composed of moderately compact or nearly transparent ice. The first effect of the sun shining on the surface is to convert the superficial crust into a mass of crumbling ice filled with cavities, so nearly opaque that it protects the interior of the mass from any but the most trifling influence of luminous heat, and absolutely cuts off all obscure radiation. Only when the superficial crust has been washed away by heavy rain, and before the sun has again acted on the surface, do we find blue ice, more or less compact, appearing on the surface. It has |