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ITH Baron von Humboldt, says the late Professor Louis Agassiz, "ends a great period in the history of science: a period to which Cuvier, Laplace, Arago, Gay-Lussac, De Candolle and Robert Brown belonged." It was a period of tireless research, of important discoveries, of brilliant generalizations. It was a period in which the specialist appeared, and secured for himself an honorable position. Yet there were men, and among them Humboldt the most distinguished of them all, who were deeply interested in all departments of science, men who sought to master at least their elementary principles and to render themselves able to judge intelligently concerning the conclusions which were reached. Since Humboldt passed away it is doubtful if any one has lived who in the extent and accuracy of his knowledge, the breadth of his vision and the soundness of his judgment can be compared with him as an equal. All the more true is it that his death in 1859 closed an era in the scientific world.

It was in this year that Charles Darwin published "The Origin of Species" and that the Fraunhofer lines of the spectrum were discovered. The theory of evolution was the outcome of studies which Darwin's book compelled the scientific world to undertake. With the full, or even partial, acceptance of that theory new methods of study have been introduced into nearly every department of learning. In the face of such a theory it has been impossible to be satisfied with the old views of history, literature, philosophy, theology, to say nothing of science. It is therefore a matter of no little interest to know what were the views of Humboldt and his co-laborers during the period above mentioned, upon which the foundation of a new era was built. For a clear and accurate statement of the scientific knowledge of his time no work is more worthy of confidence than Humboldt's "Cosmos", of which Vol. I. was published in 1845, Vol. II. in 1847, Vol. III. in 1850, Vol. IV. in 1858 and Vol. V. soon after the author's death. The earlier editions were constantly improved, and the entire edition, furnished with notes, containing extracts from private letters or publications of distinguished men which are of great interest and value, has appeared again and again. Admitting, as we must admit, that many, perhaps most of the conclusions reached in this work, have been set aside by later discoveries, the