The Cause of An Ice Age

gh even to him they will doubtless be often useful in supplying references, or suggesting lines of research. Bach book will be complete in itself, care, however, being taken that while the books do not overlap, they supplement each other ; and while scientific in treat ment, they will be, as far as possible, presented in simple language, divested of needless technicalities. The rapid progress of science has made it more and more difficult, and renders it now quite impossible, to master the works which appear, almost daily, on various branches of science, or to keep up with the proceedings of our numerous Scientific Societies. A distinguished statesman has recently expressed the opinion, that we cannot expect in the next fifty years any advance in science at all comparable to that of the last half - century. Without wishin yi EDITOR'S INTRODUCTION. should be disposed to hope that in the future the prog ress of science will be even more rapid. In the first place, the number of students is far greater; in the second, our means of research the microscope and telescope, the spectroscope, photography, and many other ingenious appliances are being added to and rendered more effective year by year ; and, above all, the circle of science is ever widening, so that the farther we advance the more numerous are the problems opening out before us. No doubt there are other Scientific Series, but it is not believed that the present will exactly compete with any of them. The International Scientific Series and Nature Series are no doubt useful and excellent, and some of the volumes contained in them would well carry out the ideas of the Publishers, but, as a rule, they are somewhat more technical and go into minuter de tails. The names of the Authors are a sufficient guarantee that the subjects will be treated in an interesting and thoroughly scientific manner. HIGH ELMS, FARNBOROUGH: November, 1891. PEEFACE. As I have written an Introduction to account for the appearance of this book, I have nothing further to say on that subject. I have only to discharge here the pleasant duty of expressing my thanks to the many friends who have helped me in various ways and degrees by kindly coun sel and friendly remonstrance. Their names are Dr. V. BALL, Eev. M. H. CLOSE, Rev. Dr. CROSSKEY, Prof. G. F. FITZGERALD, Prof. C. LAPWORTH, Sir J. LUB BOCK, Mr. A. EAMBAUT, Prof. W. SOLLAS, and Mr. L. STEELE. ROBERT S. BALL. OBSERVATORY, COUNTY DUBLIN, November 14, 1890. CONTENTS. CHAPTER PAGE INTRODUCTION xi I. THE RECORDS OF THE ICE 1 II. THE SUCCESSION OF GLACIAL AND GENIAL PERIODS . 27 III. ATTEMPTS TO SOLVE THE PROBLEM OF GLACIATION . 39 IV. THE PERTURBATIONS OF THE EARTH'S ORBIT . . 60 V. THE ASTRONOMICAL THEORY OF THE ICE AGE . . 78 VI. THE REASON WHY THIS BOOK HAS BEEN WRITTEN . 112 VII. How THE ASTRONOMICAL THEORY is CORROBORATED . 138 VIII. CONCLUDING CHAPTER 150 APPENDIX 175 INDEX 179 INTKODTJCTION. WE are to discuss in the following pages some of those revolutions of which in ages past our earth has been the scene. Perhaps it would be rather more cor rect to say thjat we are to discuss a whole series of revolutions, each of which bears a general resemblance to the rest. The date at which our story opens is a very remote one judged by ordinary historical standards. There is not even a tradition to which we might refer which would give the slightest record of these great events ; yet when viewed from a geological standpoint the phenomena with which we shall have to