320 cosmos. 



he first directed toward the mountainous parts of the moon, 

 and showed how their summits might be measured, while he, 

 like Leonardo da Vinci and Mostlin, ascribed the ash-colored 

 light of the moon to the reflection of solar light from the earth 

 to the moon. He observed with low magnifying powers the 

 group of the Pleiades, the starry cluster in Cancer, the Milky 

 Way, and the group of stars in the head of Orion. Then fol- 

 lowed, in quick succession, the great discoveries of the four 

 satellites of Jupiter, the two handles of Saturn (his indistinct- 

 ly-seen rings, the form of which was not recognized), the solar 

 spots, and crescent shape of Venus. 



The moons of Jupiter, the first of all the secondary planets 

 discovered by the telescope, were first seen, almost simulta 

 neously and wholly independently, on the 29th of December, 

 1609, by Simon Marius at Ansbach, and on the 7th of Jan- 

 uary, 1610, by Galileo at Padua. In the publication of this 

 discovery, Galileo, by the Nunchis Siderius (1610), preced- 

 ed the Mundus Jovialis (1614) of Simon Marius,* who had 



on our earth." The comparison is remarkable, since, according to Ric- 

 cioli, very exaggerated ideas of the height of our mountains were then 

 entertained, and one of the principal or most celebrated of these ele- 

 vations, the Peak of Teneriffe, was first measured trigonometrically, 

 with some degree of exactness, by Feuillee, in 1724. Galileo, like all 

 other observers up to the close of the eighteenth century, believed in 

 the existence of many seas and of a lunar atmosphere. 



* I here again find occasion (Cosmos, vol. i., p. 185) to refer to the 

 proposition laid down by Arago : " The only rational and just method 

 of writing the history of science is to base it exclusively on works, the 

 date of whose publication is certain. All beyond this must be confused 

 and obscure." The singularly-delayed publication of the Frunkische 

 Kalender or Practica (1612), and of the astronomically important mem- 

 oir entitled " Mttndus Jovialis anno 1609 delectus ope perspicilli Bel- 

 gici (February, 1614)," may indeed have given occasion to the suspicion 

 that Marius had drawn his materials from the Nuncius Siderens of Gal- 

 ileo, the dedication of which is dated March, 1610, or even from ear- 

 lier manuscript communications. Galileo, irritated by the still remem- 

 bered lawsuit against Balthasar Capra, a pupil of Marius, calls him the 

 usurper of the system of Jupiter, " Usurpatore del sistema di Giove," 

 and he even accuses the heretical Protestant astronomer of Gunzen- 

 hausen of having founded his apparently earlier observation on a con- 

 fusion between the calendars. " Tace il Mario di far cauto il lettore, 

 come essendo egli separato delta chiesa nostra, ne avendo accettato 

 l'e'mendatione Gregoriana, il giorno 7 di gennaio del 1610, di noi Cat- 

 tolici (the day on which Galileo discovered the satellites) e Pistesso, 

 che il di 28 di Decembre del 1609, di loro eretici, e questa e tutta la 

 precedenza delle sue finte osservationi" (Ventui-i, Memoire e Lettere di 

 G. Galilei, 1818, Part i., p. 279 ; and Delambre, Hist, de I'Astr. Mod. t 

 t. i., p. 696). According to a letter written by Galileo in 1614 to the 

 Accademia di Lincei, it would appear that he attempted, somewhat un- 

 philosophically, to direct his complaint against Marius to the Marchese 



