For EIGHT DOLLARS remitted directly to the Publishers, the LIVING AGE will be punctually forwarded for a year, free of postage. Remittances should be made by bank draft or check, or by post-office money-order, if possible. If neither of these can be procured, the money should be sent in a registered letter. All postmasters are obliged to register letters when requested to do so. Drafts, checks, and money-orders should be made payable to the order of LITTELL & CO. Single copies of the LIVING AGE, 18 cents. THE SILENT PIPES. THEY'LL raise the reel and rant no more, Nor play the springs they played of yore, When lads and lasses tripped the floor From gloamin' until early; No more a bridal lilt they'll blow, Or wailing coranach, although Death's hand should lay a kinsman low, The pipes that played for Charlie. Glenfinnan heard their joyful note, And distant straths and hills remote, When in the Northern air afloat The Royal flag waved fairly; They blew a welcome to Lochiel, And many a chieftain's heart of steel Beat high to hear the warlike peal Of pipes that played for Charlie. Oh! lightly marched the Highland host, The pipes that played for Charlie. They sang fu' low at Holyrood Whose smiles the prince lo'ed rarely; They blew a last, a mournful strain, Of pipes that played for Charlie. NIMMO CHRISTIE. WESTWARD. WESTWARD the sunset is dying, The way that the Summer has flown Flying, flame-crowned and crested With light from the day that is spent, After the Summer that rested Awhile in our meadows - and went. Westward the breezes are blowing And breathing of nothing but rest; Thy home is there in the west, Ah, dreary and darkly and slow drifts BALLADE OF RYDAL VALE. I. So as of old the wandering Greek, Of breezes blown from Araby; II. You've climbed the Himalayan peak By many a soft New England dale You've wandered, yet you scarce could see A fairer place than Rydal Vale. III. Oh! stream of winding curve and creek, Friend, 'tis a question of degree. A fairer place than Rydal Vale! Longman's Magazine. From The Fortnightly Review. BY ALFRED R. WALLACE. he has brought together all the facts bearing on the problem, and has arrived at certain definite conclusions of the greatest interest. The object of the present article is to give a popular account of so much of his work as bears upon the question of the thickness and density of the earth's crust and the constitution of the interior.1 harmonize and explain. But for many years past a good practical geologist, who is also an advanced mathematician FEW Scientific inquiries excite greater - the Rev. Osmond Fisher- has made interest than those recent researches this subject his speciality, and in a most which have so greatly extended our interesting volume, of which a second knowledge of the stars and nebulæ, and carefully revised edition, with an whether by determining the direction appendix, has been recently published, and velocity of their motions, or ascertaining their physical constitution and probable temperature. In comparison with this considerable amount of knowledge of such distant bodies, it seems strange that so little comparatively is known of the structure and internal constitution of the globe on which we live, and that much difference of opinion should still exist on the fundamental question whether its interior is liquid the evidence in favor of the view that, or solid, whether it is intensely hot or comparatively cool. Yet the definite solution of this problem is a matter of the greatest theoretical interest, since it would not only elucidate many geological phenomena, but might possibly serve as a guide in our interpretation of appearances presented by the other planets and even by more remote bodies; while it is not unlikely that it may soon become a practical question of the highest importance, inasmuch as it may lead us to the acquisition of a new source of heat, in many ways superior to that produced by the combustion of fuel, and practically inexhaustible. It is only during the present century that facts have been accumulating in various directions, bearing more or less directly on the question of the earth's internal condition. These have been partially dealt with, both by geologists and by physicists; but the problem is such a complex one, and the evidence of so varied a nature and often so difficult to interpret, that the conclusions reached have been usually doubtful and often conflicting. This seems to have been due, in part, to the fact that no properly qualified person had, till quite recently, devoted himself to a thorough study of the whole subject, taking full account of all the materials available for arriving at a definite conclusion, as well as of the various groups of phenomena which such a conclusion must We will first consider the nature of The below a superficial crust, there is a There are also very important evidences of internal heat derived from the universal phenomenon of a fairly uniform increase of temperature in all deep wells, mines, borings, or tunnels. This increase has been usually reckoned as 1° F. for each sixty feet of descent, 1 Physics of the Earth's Crust, by the Rev. Osmond Fisher, M.A., F.G.S. Second edition, altered and enlarged. Macmillan and Co., 1889. With an Appendix, 1891. but a recent very careful estimate, by nal liquidity was almost wholly abanProfessor Prestwich, derived from the doned. But this argument has now whole of the available data, gives 1° F. been shown to be erroneous by the for every 47.5 feet of descent. It is a more complete investigations of Procurious indication of the universality of fessor George Darwin, while Sir William this increase that, even in the coldest Thomson (now Lord Kelvin) has reparts of Siberia, where the soil is frozen cently shown experimentally that a to a depth of six hundred and twenty rotating liquid spheroid behaves under feet, there is a steady increase in the stresses as if it were a solid. Another temperature of this frozen soil from the difficulty arises from the phenomena of surface downwards. Much has been the tides. It has been argued that, if made by some writers of the local differ- the interior of the earth is liquid, tides ences of the rate of increase, varying will be formed in it which will deform from 1o in twenty-eight feet to 1° in the crust itself, and thus, by lifting the ninety-five; and also of the fact that in water up with the land, do away with some places the rate of increase dimin- any sensible tides in the ocean. But ishes as the depth becomes greater.1 Mr. Fisher has pointed out that this But when we consider that springs conclusion rests on the assumption that often bring up heated water to the surface in countries far removed from any seat of volcanic action, and the extent to which water permeates the rocks at all depths reached by man, such divergences are exactly what we might expect. Now this average rate of increase, if continued downwards, would imply a temperature capable of melting rock at about twenty miles deep, or less, and we shall see presently that there are other considerations which lead to the conclusion that this is not far from the average thickness of the solid crust. the liquid interior, if it exists, is not an expansible fluid; and he shows that if this assumption is incorrect it is quite possible that little or no deformation would be caused in the crust by tides produced in the liquid interior; and he further maintains, as we shall see further on, that all the evidence goes to prove that it is expansible. Moreover, in a late paper, he claims to have proved that even the deformation of the crust itself would not obliterate the ocean tides, but would diminish them only to the extent of about one-fifth.2 There remain the geological objections founded on the behavior of volcanoes, which is supposed to be inconsistent with a liquid interior as their effective cause. We have, for instance, the phenomenon of a lofty volcano like Etna pouring out lava from near its summit, while the much lower volcanoes of Vesuvius and Stromboli show no corresponding increase of activity; and the still more extraordinary case of Kilauea, on the lower slopes of Mauna Loa at a height of about thirty-eight hundred feet, whose lake of perennial liquid lava suffers no alteration of level or any increased activity when the parent mountain is pouring forth lava from Before going further it will be well to consider certain objections to this conclusion, which for a long time were considered insuperable, but which have now been shown to be either altogether erroneous or quite inconclusive. In Sir Charles Lyell's "Principles of Geology," Mr. Hopkins is quoted as having shown that the phenomenon of the precession of the equinoxes, due to the attraction of the sun and moon on the equatorial protuberance, requires the interior of the earth to be solid, or at least to have a crust not much less than one thousand miles thick. This view was supported by Sir William Thomson and other eminent mathematicians, and so great was the faith of geologists in a height of fourteen thousand feet. these calculations that for nearly forty years the theory of the earth's inter 1 In a recent deep boring at Wheeling, Virginia, the rate of increase was found to be greater as the depth increased. Again it is argued that if the igneous products of volcanoes are derived from one central reservoir there ought to be 2 Proceedings of the Cambridge Philosophical Society, 1892. |