816 cusMus. 



as solid bodies of material thickness, but merely ah ^deal ab- 

 stractions. It is more certain that in the middle of the six- 

 teenth century, when the theory of the seventy-seven homo- 

 centric spheres of the learned writer, Girolamo Fracastoro. 

 found general approval ; and when, at a later period, the op' 

 ponents of Copernicus sought all means of upholding the Ptol- 

 emaic system, the idea of the existence oi solid spheres, circles, 

 and epicycles, which was especially favored by the Fathers of 

 the Church, was still very widely diffused. Tycho Brahe ex- 

 pressly boasts that his considerations on the orbits of comets 

 first proved the impossibility of solid spheres, and thus destroy- 

 ed the artificial fabrics. He filled the free space of heaven 

 with air, and even believed that the resisting medium, when 

 disturbed by the revolving heavenly bodies, might generate 

 tones. The unimaginative Rothmann believed it necessary 

 to refute this renewed Pythagorean myth of celestial harmony. 

 Kepler's great discovery that all the planets move round 

 the sun in ellipses, and that the sun lies in one of the foci of 

 these ellipses, at length freed the original Copernican system 

 from eccentric circles and all epicycles.* The planetary struc- 

 ture of the world now appeared objectively, and as it were 

 architecturally, in its simple grandeur ; but it remained for 

 Isaac Newton to disclose the play and connection of the intern- 

 al forces which animate and preserve the system of the uni- 

 verse. We have already often remarked, in the history of the 

 gradual 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 fi.nd this phenomenon most strikingly 

 manifested in the first ten years of the seventeenth century ; 

 for Tycho Brahe (the founder of modern astronomical calcula- 

 tions), Kepler, Galileo, and Lord Bacon, were cotemporaries. 

 All these, with the exception of Tycho Brahe, were enabled, 

 in the prime of life, to benefit by the labors of Descartes and 

 Fermat. The elements of Bacon's Instauratio Mag7ia ap- 

 peared in the English language in 1605, fifteen years before 



* A better insight into the free movement of bodies, and into the in- 

 dependence of the direction once given to the earth's axis, and into th<* 

 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 

 Revolut. Orb. C(El-,\\h. i., cap. 11, triplex motus telluris). The parallel- 

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

 sun, in conformity with the law of inertia, withr ut the application of a 

 correctinff eoicvcJe 



