358 THE POPULAR SCIENCE MONTHLY 



ogists, but what the Herschells, Maedler, Arago, Leverrier, Laplace, 

 Bessel of Konigsberg, 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 re- 

 volving 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 Ber- 

 zelius, the chemist, gave much time and thought. 



The first person to observe and report upon the zodiacal light, ac- 

 cording to Humboldt, was Dominique Cassini, of Bologna. He pub- 

 lished his views in 1668. About this time the phenomenon was ob- 

 served 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 pow- 

 erful 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 need- 

 ing no proof that the interior of the earth is liquid and of high tempera- 

 ture, 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 dis- 

 tance 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 pendu- 

 lum 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 con- 

 cerning 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 



