698 COSMOS. 



of the world now appeared objectively, and as it were archi- 

 tecturally, in its simple grandeur ; but it remained for Isaac 

 Newton to disclose the play and connection of the internal 

 forces which animate and preserve the system of the universe. 

 We have already often remarked in the history of the gra- 

 dual development of human knowledge, that important but 

 apparently accidental discoveries, and the simultaneous ap- 

 pearance of many great minds, are crowded together in a 

 short period of time ; and we find this phenomenon most 

 strikingly manifested in the first ten years of the seventeenth 

 century ; for Tycho Brahe (the founder of modern astronomic^ 

 calculations), Kepler, Galileo, and Lord Bacon, were cotempo- 

 raries. All these, with the exception of Tycho Brahe, were 

 enabled, in the prime of life, to benefit by the labours of Des- 

 cartes and Fermat. The elements of Bacon's Instauratio 

 Magna appeared in the English language in 1605, fifteen years 

 before the Novum Or g anon. The invention of the telescope, and 

 the greatest discoveries in physical astronomy (viz., Jupiter's 

 satellites, the sun's spots, the phases of Venus, and the 

 remarkable form of Saturn), fall between the years 1609 and 

 1612. Kepler's speculations on the elliptic orbit of Mars,* 

 were began in 1601, and gave occasion, eight years after, to 

 the completion of the work entitled Astronomia nova sett 

 Physica celestis. " By the study of the orbit of Mars," 

 writes Kepler, " we must either arrive at a knowledge of the 

 secrets of astronomy, or for ever remain ignorant of them. 

 I have succeeded, by untiring and continued labour, in sub- 

 jecting the inequalities of the movement of Mars to a natural 

 law." The generalization of the same idea led the highly- 

 gifted mind of Kepler to the great cosmical truths and pre- 

 sentiments which, ten years later, he published in his work 

 entitled Harmonices Mundi libri quinque. " I believe," he 

 well observes in a letter to the Danish astronomer Longo- 



rotatory and progressive movement of the terrestrial planet in its orbit, 

 has freed the original system of Copernicus from the assumption of a 

 declination-movement, or a so-called third movement of the earth (De Re- 

 volut. orb. cod., lib. i. cap. 11, triplex motus telluris.) The parallelism, 

 of the earth's axis is maintained in the annual revolution round the 

 sun, in conformity with the law of inertia, without the application of a 

 correcting epicycle. 



* Delambre, Hist, del' Astronomic ancienne, t. ii. p. 381. 



