ogists, but what the Herschells, Maedler, Arago, Leverrier, Laplace, Bessel of Königsberg, an authority on comets, and Faye, discovered and taught. Aerolites, shooting stars, fire balls, meteoric stones, are given extensive treatment. Aerolites are said to be "small bodies revolving with planetary velocity, and in obedience to the law of general gravity, in conic sections round the sun." Showers of shooting stars were observed by Humboldt and his companions in Cumana, S. A., in 1799 and in 1832-33 by Professor Denison Olmstead, of New Haven, Ct. To the consideration of this phenomena men like Brandes, Benzenberg, Bessel, Arago, Eduard Biot, Poisson, the mathematician, and Berzelius, the chemist, gave much time and thought.
The first person to observe and report upon the zodiacal light, according to Humboldt, was Dominique Cassini, of Bologna. He published his views in 1668. About this time the phenomenon was observed in Persia by Chardin, the traveler. Laplace, Schubert, Poisson and Sir John Herschell regarded the phenomenon with deep interest and sought a satisfactory solution for it. From Sir John Herschell at the Cape of Good Hope came the suggestion that the milky way could be broken up into well-defined sections and that with sufficiently powerful telescopes all its nebulae could be resolved into stars. Humboldt himself directs attention to so-called "starless openings" in the milky way through which one looks out into empty space.
Before Humboldt died there were a large number of competent observers of terrestrial phenomena. It was taken for granted as needing no proof that the interior of the earth is liquid and of high temperature, and that this heated melted matter has acted, and continues to act, upon the surface of the earth. It was believed that the depths of the sea correspond in general with the heights of the mountains, and that our power to study the surface of the earth is limited to about the distance of 48,000 feet. The history of volcanoes, traced from the days of Plato, Aristotle, Ovid, Pliny to Daubeny, whose treatise on the subject (Paris, 1848) Humboldt accepts as the best ever written, leads him to propound opinions of his own and to compare them with suggestions made by Darwin in his account of his cruise in the ship Beagle. He places a high estimate on the value of the measurements by the pendulum of Sir Edward Sabine as a means of determining the figure of the earth. From his voyage in 1822 and 1823 much was learned about magnetism in general and terrestrial magnetism in particular. To the establishment of what were deemed by Humboldt sound theories concerning the internal heat of the earth, Fourier, Biot, Laplace and Poisson made large contributions. The mathematical calculations of Friedrich Gauss and Weber were accepted as of the first importance in the study of magnetism. The oscillations of the magnetic needle were observed and noted in different parts of the world. Humboldt himself says in a note. Vol. I., p. 187: "I regard the discovery of the law of the
