110 LIFE AND WORKS OF KEPLEK. 



accepted unaffectedly, without luuriiuuing or re])iiiiiig-, tlie labors and 

 einployuients, whatever they might be, which would aid him in the 

 sustenance of his family. 



The laws of Kei)ler are the solid and impregnable foundation of modern 

 ostronomy, the immutable and eternal rule of the displacement of the 

 heavenly bodies in space; no other discov'ery, perhaps, has better justi- 

 fied the words of the sage: He who increases knowledge increases labor ; 

 no other has given birth to more numerous researches aud greater dis- 

 coveries; but the long and laborious route v/hich led to it is known but 

 to the few. None of the numerous writings of Kepler are regarded as 

 classical; his renown alone will be immortal; it is written in the heav- 

 ens ; the i)rogTess of science can neither diminish nor obscure it, and 

 the planets, by the always constant succession of their regular move- 

 ments, will proclaim it from age to age. 



[Note. — Nothing is wanting to the completeness of the above memoir ; but, having 

 been addressed iu tlie first instance to an assembhige of men of scicncij, the learned 

 author has probably thought it superlluons to give so distinct aud formal a statement 

 of the three laws, as they are called, of Kepler, (BcguUe KcpJcri,) as it may be convenient 

 for the general reader to have beneath his eye. For this reason, the following brief 

 exposition of those celebrated astronomical axioms is hero transcribed from the Ency- 

 clopedia Americana. — Tr. 



" The first of these laws is that the planets do not move, as Copernicus had imagined, 

 in circles, but in ellipses, of which the sun is in one of the foci. For this, Kepler was 

 indebted to the observations which Tycho had made on the planet Mars, Avliose eccen- 

 tricity is considerable, and agrees particularly with the rule; in determining which 

 Kepler went through an indescribably laborious analysis. The second law is, tltat an 

 imaginai'y straight line from the sun to the planets, radius rector, always describes 

 equal sectors iu equal times. By this rule Kepler calculated his tables, imagining the 

 whole plane of revolution divided into a number of such sectors, and, from this, he 

 investigated their respective angles at the sun. This was called KejyJcr's ■problem. The 

 third law teaches that, in the motion of the j)h^nets, the squares of the times of revo- 

 lution are as the cubes of the mean distances from the sun ; one instance of the appli- 

 cation of which law, in the want of other means, is in the determination of the distance 

 of the planet Herschel from the sun, it having been ascertained that its time of revolu- 

 tion amounts to a little more than eighty-two years." 



