PREFACE. 



One of the most noticeable of common experiences is the acknowledged 

 absence of intelligent and well-defined knowledge of the world in which we 

 live. Nor is this an indication of illiteracy by any means, for in this ab- 

 sorbing and engrossing age only those who live lives of scholastic study or 

 abundant leisure can keep abreast of the teeming press. The very abund- 

 ance of the books relating to the history of the world and its inhabitants 

 discourages rather than invites investigation ; for, while each writer dis- 

 cusses his chosen specialty, and confines his researches to some particular 

 department of travel or exploration, he who would get at the general results 

 and gain from them a comprehensive view of the whole field, is appalled at 

 the outset by the abundance rather than the paucity of books which claim 

 his attention. The things which attract and interest one explorer are passed 

 over completely by another; and so it happens that while one writer devotes 

 himself to the natural history of the country, or countries, which he visits, 

 another will deal with the descriptive geography and material resources, 

 another with the manners and customs of the people, another with the 

 physical geography and climatic conditions and limitations, and still another 

 with the commercial possibilities and international relations. But the business 

 or professional man, the merchant, mechanic, or farmer, has no time to follow 

 each traveler or writer as he roams at will among his chosen fields of ex- 

 ploration, or describes at length the results of his labors. The practical 

 results he would gladly become acquainted with, but he can not search for 

 them amid a mass of comparatively unimportant details, whose mastery would 

 require a life-time of scholastic leisure. This work of sifting out practical 

 facts and important general laws, and arranging them in the order and sequence 

 in which they naturally belong, if done at all, must be done for him, and that 

 is precisely what the. present work aims to do. The two forces in nature which 

 more than any others, more, even, than all others, affect and determine the 

 conditions of living and the range of productions, are heat and cold — the Polar 

 and Tropical Worlds. A knowledge of the working of these forces furnishes 

 the key to those climatic changes which are ever going on, and shows how 



