PHYSICS OF THE EARTH'S CRUST.. BY THE REV. OSMOND FISHER, M.A., F.G.S., ་་ RECTOR OF HARLTON, HON. FELLOW OF KING'S COLLEGE, LONDON, AND LATE [The Right of Translation and Reproduction is reserved.] PREFACE. FOR many years past I have been convinced that various questions of Physical Geology might be answered negatively, if not positively, by applying to them simple mathematical reasoning, and quantitative treatment. My own views have, in some respects, been greatly altered by the application of this method; and I confess that the present work contains within itself evidence of the circumstance; for not only will it be found that the views now put forward differ in some respects from those which I have previously published in contributions to scientific periodicals; but the effect of the progressive application of the quantitative method may be traced in the book itself; and the development of ideas, proposed in the earlier chapters, will sometimes be found to have taken an unexpected turn later on. This remark applies especially to certain hypotheses, which at first presented themselves in a favourable light, to account for compression and for the formation of ocean basins. It is extremely probable that, if these investigations are carried further, some of the theories now offered as fairly established, may turn out to be untenable. With a growing science like Geology this is unavoidable. On a review of what I have written, I feel how many difficulties have been left unsolved, and some which have occurred to me not even mentioned. Nevertheless I hope that this attempt will not be without a certain value in advancing the study of the Physics of the Earth's Crust. The mathematical reader will perhaps be surprised by the rough and ready mode of treatment adopted in some instances. But when it is recollected that, for the most part, we can assign only very hypothetical values for our symbols, it would be affectation to seek close results, which would after all have no greater value than those which claim to be only distant approximations. The course of the argument and the general conclusions, will be found repeated in the Summary at Chapter XXII. But it is hoped that a perusal of this may not be substituted for reading the book. It is believed that the reasoning of the several chapters will be found intelligible, even without wading through the calculations. My thanks are due to the Councils of the Geological Society of London, and of the Philosophical Society of Cambridge, for permission to make free use of papers contributed by me to their publications. I have similar acknowledgments to make to the Proprietors of the Philosophical Magazine, the Geological Magazine, and the Quarterly Journal of Science. My kind friends, H. W. BRISTOW, Esq., F.R.S., Senior Director of the Geological Survey, and A. F. GRIFFITH, Esq., B.A., of Lincoln's Inn, Scholar of Christ's College, Cambridge, have rendered me most valuable help in revising the proofs while they were passing through the press. HARLTON RECTORY, 18 October, 1881. OSMOND FISHER. CONTENTS. The rise of temperature on descending into the earth-The causes which have been assigned for it-Attempts to determine the law of increase by observation— Their results-Deep bore-hole at Sperenberg and methods of observation used there-General effects of convection currents in a bore-hole-Tabulated obser- vations at Sperenberg-Anomalous result supposed to be deducible therefrom- Anomaly explained—General law of average rise of temperature not impaired thereby-Hot springs and volcanos prove that the rise of temperature con- tinues, but do not inform us whether the law near the surface obtains unaltered Little known about the condition of the interior of the earth-Results of the mathe- matical " Determination of the mean and surface densities-The question proposed whether the fluid condition still partially exists more or less-Connection be- tween this question and that of the law of internal temperature-Two modes of attacking the question, (1) Precession, (2) the tides-Opinions of Sir Wm. Thomson, Hopkins, Delaunay, and others—Possibility of a cooled crust resting INTERNAL DENSITIES AND PRESSURES. Speculations concerning the materials in successive couches-Waltershausen's theory-His law of density open to correction-His tables of densities and pressures-Fluid pressures within the earth calculated from Laplace's law of |