Page:Popular Science Monthly Volume 80.djvu/357

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of South and Central America and Mexico. He was the first, so it is claimed, to mark the decrease in intensity of magnetic force from the poles to the equator. At any rate, his journey to the tropical possessions of Spain in the new world gave a very decided impulse to the study of natural history.

It is not strange that a man with his extensive knowledge, his varied experience as a traveler and the resources of the scientific and literary world at his disposal should desire to write and publish a work that should set forth in clear and accurate form all that in his time was known of the earth and the celestial bodies. If any man was ever justified in the belief that he could satisfy his ambition in this respect it was Alexander von Humboldt at the age of seventy-six.

"Cosmos" is a history in outline of the physical contemplation of the universe. Its aim is to show the unity of the universe. It is not a history of the natural sciences as such, rather an attempt to point out the close connection of all the forces of nature. To do this all possible sources of information are laid under tribute. In his study of what has been done and is now known, Humboldt pledges himself to follow three laws, or to be guided in his thought and writing, by three principles: viz.,

1. To show the efforts of reason, through meditation upon phenomena to obtain a correct knowledge of natural laws.
2. To consider events which have suddenly enlarged the horizon of observation.
3. To show what has been the result in the enlargement of the fields of human knowledge through the discovery of new means of sensuous perception, or of new organs, or instruments by means of which we are brought into closer touch with terrestrial and celestial objects. Thus in the telescope and the microscope we have new organs of perception.

Starting from the basin of the Mediterranean, with its three contiguous closed seas and its three peninsulas, Spain, Italy and Greece, the discoveries made by voyages to other countries are named, and the fact stated that the earliest civilizations were developed in countries rich in rivers, as Egypt, Messopotamia, India and China. The author takes pains to emphasize the exceptional men who lead in new movements in travel, who make startling and important discoveries. Nor does he overlook the events which mark the beginning of new eras in the world's history. He has the rare faculty of making us see how striking contemporaneous events often are. For example, when Columbus discovered America, Copernicus was studying astronomy with Brudzewski in the University of Cracow. The rapid extension of knowledge at the beginning of the seventeenth century was due to the studies and discoveries of Galileo and Kepler, at its close to those of Newton and Leibnitz. It was in this century that the problems of