KD 56663 MAR 221897 Astronom. Ibs. HARVARD (The rights of translation and of reproduction are reserved) PREFACE. THE first work, devoted entirely to the study of Polar Auroras, was written in France; it is entitled Traité Physique et Historique de l'Aurore Boréale,' and was published in 1733 by De Mairan, in the 'Mémoires' of the Académie des Sciences.' We must allow a century to elapse before we find anything to be compared with it in importance and volume, when the work 'Aurores Boréales' appeared in the collection of the voyages of the Northern Scientific Commission on the corvette Recherche.' This volume, accompanied by magnificent plates of which we shall reproduce the most interesting-contains records of observations of the aurora borealis taken in Lapland during the winter of 1838-39 by Bravais, Lottin, Lillihoeoek, and Siljestroem. Bravais added general remarks on this phenomenon, and discussed the principal observations collected at that date, and the various hypotheses put forward to account for them. Since then no general work on the subject has appeared in this country. The student was obliged to consult original papers published in all languages, or foreign treatises, among which we will mention only one as the most complete, that of Hermann Fritz of Zurich, Das Polarlicht' (Leipzig, 1881). I have tried to meet this want by writing in the journal 'La Lumière Electrique' (vol. vii., last half of 1882) a series of ten articles on the Polar Aurora, accompanied by numerous plates, which reproduce from the original documents the principal appearances of the polar aurora. These articles, revised according to the most recent discoveries, have served as the basis of the present work. It would have been easy to increase considerably the size of this volume by citing a greater number of the results of observations. I thought, however, that it was better to choose for each class of phenomena two or three of the most conclusive examples, borrowed from those observers who are most worthy of confidence. I have not tried to publish all the observations collected at all times and in all countries on Polar Auroras. I have rather sought to give a sketch of the actual state of our knowledge of this question, noting the results which may be considered as defi nitely acquired, and also the points on which further research seems unnecessary. I have indicated in the course of the work the most important books and papers on each branch of the subject; but here, also, some limit was necessary. For these works must now be reckoned by hundreds, some containing merely observations of the aurora, others theories about it. A complete bibliography of the subject would alone fill a large volume. The figures in the text are reproduced directly, and as exactly as possible, from the original documents, and their source is always indicated. They are taken partly from the fine atlas of Bravais, which contains the most beautiful engravings of the aurora borealis which have yet been published. I have been able to add drawings which are less known, and some never before published. In particular, my thanks are due to M. de la Monneraye, a lieutenant in the navy, who kindly placed at my disposition a remarkable series of drawings which he executed himself in the course of a sojourn in the seas near Newfoundland. In the Appendix will be found a list of all the appearances of the aurora borealis observed from 1700 to 1890 in Europe below the 55th parallel of latitude. Above this limit auroras are so frequent that at certain epochs they may be seen almost every day. In |