The preparation of a volume on _Climate_ for The Science Series was suggested to me by the Editors in October, 1904. I was asked to prepare a book “which can be read by an intelligent person who has not had special or extended training in the technicalities of the science, ... the book to be such as would not compete with strictly meteorological text-books, but to handle the broad questions of climate.” It so happened that it was then already in my mind to prepare a book dealing with certain large relations of climate, which might serve as supplementary reading for the students in my course on General Climatology in Harvard University. The present volume is an attempt on my part to write a book which shall meet the wishes of the Editors of The Science Series and at the same time fit the needs of my students.

_Climate_ is based on lecture-notes which have been accumulating for the past ten years. It does not attempt to present any very new or original material, but it does aim to co-ordinate and to set forth clearly and systematically the broader facts of climate in such a way that, as desired by the Editors, the general reader, although not trained “in the technicalities of the science,” may find it easy to appreciate them. At the same time, the needs of the teacher and student have been kept constantly in mind, and the subject-matter has been arranged in such a way as seems best to adapt it for purposes of thorough study.

_Climate_ may be considered in a way as supplementing the first volume of Dr. Julius Hann’s _Handbuch der Klimatologie_, an English translation of which was prepared by me and published in 1903. In that book, the standard work of its kind in the world, the principles of climatology are clearly set forth. My present volume deals with matters which are either omitted altogether in the _Handbook_, or else are very briefly treated therein. _Climate_ is wholly independent of Hann’s splendid work, except in so far as my study of that book inspired me to prepare this one.

The general scope and purpose of the different sections in _Climate_ are as follows. The Introduction is essentially a very condensed synopsis of the first six chapters of Hann’s first volume, with the addition of some other matter. Chapter I gives a sketch of the classification of the zones. Chapters II and III give a brief summary of the general climatic types which result from the control of land and water, and of altitude, over the more important elements of climate. Chapters IV, V, and VI are intended to give an outline of the climatic characteristics of the zones in a simple and vivid form, with the least possible use of tabular matter. For further general information on this subject, reference may be made to the world-charts of temperature, winds, cloudiness, rainfall, etc., given with greater or less completeness in the various text-books of meteorology, and, very fully, in the _Atlas of Meteorology_. In Chapter VII the attempt is made to give a survey of some of the relations between weather and climate and a few of the more important diseases. Little information on this subject is readily accessible to the general reader. The life of man in the tropics, the temperate zones, and the polar zones is considered in Chapters VIII to X. No attempt has been made to discuss this subject in detail, for to do so would far exceed the limits set for this book. It has rather been my plan to pick out typical illustrations here and there, as suggestions. Many of the cases referred to will probably be familiar to teachers and students of geography, but the co-ordination of all the examples by climatic zones and by the natural climatic subdivisions of these zones will, it is hoped, tend to give adequate emphasis to the climatic factor, which has hitherto been much neglected. The final chapter, on changes of climate, deals with historic and periodic, and not with geologic changes. The last phase of the subject has been fully discussed in many books, while the former, which are of more interest to most persons, have received much less attention. The question of the influence of forests on climate, which many readers may expect to find considered in this book, is omitted because it is adequately taken up in Hann’s _Handbook_ (Vol. I).

I have drawn very freely upon Hann’s _Handbuch der Klimatologie_, Vols. II and III (2d ed., Stuttgart, 1897), as well as upon his _Lehrbuch der Meteorologie_ (2d ed., Leipzig, 1906), two books which are so complete in all details that every writer on meteorological or climatological subjects is inevitably very dependent upon them. The curves in Chapters IV, V, and VI were all drawn from data given in the _Lehrbuch_. In the chapters on the life of man in the different zones, I have made liberal use of Ratzel’s _Anthropogeographie_ (2d ed., Stuttgart, 1899). The principal references other than these are the following: W. M. Davis: _Elementary Meteorology_ (Boston, 1902); A. J. and F. D. Herbertson: _Man and His Work_ (London, 1899); W. Köppen: _Klimakunde. I. Allgemeine Klimalehre_ (2d ed., Leipzig, 1906); A. Supan: _Grundzüge der physischen Erdkunde_ (3d ed., Leipzig, 1903); W. Trabert: _Meteorologie und Klimatologie_ (Leipzig and Vienna, 1905); W. J. van Bebber: _Hygienische Meteorologie_ (Stuttgart, 1895); A. Woeikof: _Die Klimate der Erde_ (Jena, 1887); _Atlas of Meteorology_ (Edinburgh, 1899).

I am indebted to the publishers, Messrs. G. P. Putnam’s Sons, for their generous permission to me to use certain parts of this book in an article prepared for the _Encyclopædia Britannica_ in 1906, as well as for the privilege which they willingly accorded me of publishing as separate articles many of the chapters included in this book. Chapters I to III have appeared in the _Bulletin of the American Geographical Society_; Chapters IV to VI in the _Journal of Geography_; Chapter VII in the _Bulletin of the Geographical Society_ of Philadelphia, and