DISCOVERIES IN THE CELESTIAL SPACES. 321 



proposed to give to Jupiter's satellites the names of Sidera 

 Brandenhurgica, while Galileo preferred the names Sidera 

 Cosmica or Medicea, of which the latter found most approv- 

 al at the court of Florence. This collective appellation did 

 not satisfy the yearnings of flattery. Instead of designating 

 the satellites hy numhers, as we do at present, Marius had 

 named them lo, Europa, Ganymede, and Callisto ; but for 

 these mythological designations Galileo's nomenclature sub- 

 stituted the family names of the ruling house of Medici — 

 Catharina, Maria, Cosimo the elder, and Cosimo the younger. 

 The knowledge of Jupiter's satellite-system, and of the 

 phases of Venus, has exercised the most marked influence on 

 the establishment and general diffusion of the Copernican sys- 

 tem. The little world of Jupiter (Mzmdus Jovialis) present 

 ed to the intellectual contemplation of men a perfect image 

 of the large planetary and solar systems. It was recognized 

 that the secondary planets obeyed the laws discovered by Kep 

 ler ; and it was now first observed that the squares of their 



di Braudeburgo. On the whole, however, Galileo continued well dis- 

 posed toward the German astronomers. He writes, in March, 1611, 

 '* Gli ingegni singolari, che in gi'an uumero fioriscono nell' Alemagua, 

 mi hauno lungo tempo tenuto in desideno di vederla" {Opere, t. ii., p. 

 44). It has always appeared veiy remarkable to me, that if Kepler, 

 in a conversation with Marius, was playfully adduced as a sponsor for 

 these mythological designations of lo and Callisto, there should be no 

 mention of his countryman either in the Commentaiy published in 

 Prague, in April, 1610, to the Nuncius Siderius, miper ad mortales a 

 GalilcEo missus, or in his letters to Galileo, or in those addressed to the 

 Emperor Rudolph in the autumn of the same year ; but that, on the 

 contrary, Kepler should every where speak of " the glorious discovery 

 of the Medicean stars by Galileo." In publishing his own observations 

 on the satellites, from the 4th to the 9th of September, 1610, he gives 

 to a little memoir which appeared at Frankfort in 1611, the title, ^^ Kep- 

 leri Narratio de ohservatis a se quatuor Jovis satellitibus erronibus quos 

 Galilceus Mathematicus Florentinus jure inventionis Medicea Sidera nun- 

 cupavity A letter from Prague, October 25, 1610, addressed to Galileo, 

 concludes with the words " neminem habes, quem metuas amulum." 

 Compare Venturi, Part i., p. 100, 117, 139, 144, and 149. Misled by a 

 mistake, and after a very careless examination of the valuable manu- 

 scripts preserved at Petworth, the seat of Lord Egremont, Baron von 

 Zach asserted that the distinguished astronomer and Virginian traveler, 

 Thomas Hariot, had discovered the satellites of Jupiter simultaneous- 

 ly with, or even earlier than Galileo. A more careful examination of 

 Harlot's manuscripts, by Rigaud, has shown that his observations be- 

 gan, not on the 16th of January, but only on the 17th of October, 1610, 

 nine months after Galileo and Marius. (Compare Zach, Corr. Asiron., 

 vol. vii., p. 105. Rigaud, Account of Harriotts Asiron. Papers, Oxf., 

 1833, p. 37 ; Brewster, Martyrs of Science, 1846, p. 32.) The earliest 

 original observations of Jupiter's satellites made by Galileo and hifl 

 pupil Renieri were only discovered two vears ago. 



O 2 



