published in 1790, which first led naturalists to consider the question. Goethe's work was very little read at first, and he had great difficulty in finding a publisher for it, for it was thought that a poet could not know much of science; but the great Swiss botanist, Auguste de Candolle (born 1778, died 1841) seeing what a new light it threw upon the study of plants, taught it in his works, and then it became gradually known as one of the greatest discoveries in modern botany.

Alexander von Humboldt studies the Lines of Equal Heat over the Globe-Founds the Study of Physical Geography-Writes the 'Cosmos,' 1793-1859.-While Goethe was studying plants at Weimar, and learning the secrets of Nature in the quiet of his own home, another man of whom we must now speak, was planning to travel in distant countries, and to write a history, as far as he was able, of the work which Nature is doing all over the world.

Alexander von Humboldt, who forms a link between the science of the eighteenth and the nineteenth centuries, was born at Berlin in 1769, and was educated (together with his brother William, the great politician) at the University of Göttingen. At the age of one-and-twenty he went to Freyberg, where he was a pupil of Werner. It was at this time, when he was only just of age, that he formed the plan in his mind of spending his life in studying the works of Nature, and writing a 'grand and general view of the Universe.'

The first sketch of his book, which he called 'Cosmos,' or 'The Universe,' was written in 1793, when he was only twenty-four; and the last sheets were printed in 1859, when he was ninety years of age. In the sixty-six years between these two dates he collected and published in popular

CH. XXXVII.

HUMBOLDT'S TRAVELS.

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language an immense number of facts about nature in all parts of the world.

His chief voyage was to America in 1799, when he spent six years in Mexico, and along the shores of the Orinoco. Here he began one of his greatest undertakings, namely finding out the climate of different parts of the world, and tracing out isothermal lines, or lines of equal heat over the globe, showing what countries have the same average temperature, and explaining why some enjoy an almost equable climate all the year round, while others are very hot in summer and cold in winter. For example, he pointed out that Greenland is much colder than Lapland, even in places which are on the same line of latitude, because a cold current from the North Pole flows past Greenland, while the warm Gulf Stream crosses over from the Gulf of Mexico and washes the shores of Lapland. The importance of this study of variations of temperature was first pointed out by Humboldt, and it should be remembered as one of his most original investigations.

Again, in his long journeys through South America, he traced everywhere the different species of plants which grew at various heights, even up to 20,000 feet on the slopes of the Andes. This led him to try and find the reasons why certain plants are only to be found in certain areas, in the same way that Buffon had worked out the distribution of animals. When he returned to Paris in 1804 he had collected an immense number of facts as to the heights of mountains, the climate of countries, the minerals and metals found in them, the active and extinct volcanoes, the nature of the rocks and soils, the vegetation and the animals; and with the help of the best scientific men in Paris (each

undertaking his own special science) he published twentyeight large volumes, which contained the conclusions based upon the facts he had learnt in his travels.

In 1827 he returned to Berlin, and was then invited by the Emperor of Russia to go on a journey into the Russian provinces of Asia, where he spent nine months making the same kind of observations that he had made in America. In 1830 he was sent to Paris as Prussian ambassador, and it was not till he returned to Berlin some years after, that he began to publish the 'Cosmos' he had been preparing for so long.

In this grand work he gives a complete history of astronomy, and all the discoveries in it made up till his time; and then taking our own world as part of the universe, he describes the changes which are going on now, or have been going on in past time, on the face of the earth. It is to Humboldt that we owe much which makes geography interesting. The study of the surface of the globe, of mountain-chains, table-lands, and rivers, the climates of countries, the different winds which blow, and the currents which cross the ocean; the way in which plants and animals are distributed over the world; the different races of men, and how they have spread over the globe-all these and other facts which make geography something more than a mere list of names, Humboldt studied during his various journeys, and related them with a freshness which had a peculiar charm.

It was not so much that he advanced any one branch of science as that he led men to look upon the earth and the universe as one vast whole, and to find a living interest in every part of it. In 1858 the last sheets of the 'Cosmos' were put into the publisher's hands, but Humboldt did not

CH. XXXVII.

DEATH OF HUMBOLDT.

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live to see them finished. He had done his part: the work he had proposed to himself was completed, and he fell peacefully asleep on the 6th of May, 1859.

Chief Works consulted.-Goethe's 'Euvres Scientifiques;' Faivre ; Asa Gray's 'Botany; L. Agassiz's 'Centenary Address on A. von Humboldt;' Humboldt's 'Cosmos.'

CHAPTER XXXVIII.

SCIENCE OF THE NINETEENTH CENTURY (CONTINUED).

The three Naturalists, Lamarck, Cuvier, and Geoffroy St.-HilaireCuvier begins the Museum of Comparative Anatomy-Lamarck's History of Invertebrate Animals—Geoffroy St.-Hilaire brings Natural History Collections from Egypt-Lamarck on the Development of Animals-Geoffroy St.-Hilaire on 'Homology,' or the similarity in the parts of different Animals-Cuvier's 'Règne Animal,' and his Classification of Animals-Cuvier on the perfect agreement between the different parts of an Animal-He studies and restores the remains of Fossil Animals-His 'Ossemens Fossiles '-Death of Cuvier-Von Baer on the study of Embryology-His History of the Development of Animals, 1828.

Lamarck-Cuvier-St.-Hilaire.-When Humboldt visited Paris in 1804 there were three men holding professorships in the Museum of Natural History in that city, who had afterwards a great influence upon the study of the science of living beings. These three men were Lamarck, professor of zoology; Geoffroy St.-Hilaire, his fellow-professor; and Cuvier, assistant-professor of comparative anatomy.

The early part of the nineteenth century was, as you will remember, a very troubled time for France. The first Napoleon was carrying war and desolation all over Europe, and Paris was kept in a constant state of turmoil for many years. During all this time it is interesting to see how steadily and quietly the three men I have mentioned pursued their search after knowledge. Geoffroy St.-Hilaire