GALILEO. 109 



whose orb 



Through optic glass the Tuscan artist views 

 At evening, from the top of Fesole\ 

 Or in Valdarno, to descry new lands, 

 Rivers, or mountains in her spotty globe. 



These fresh discoveries were as unpalatable to the Aristoteleans as the 

 confutations of their master's physics, for, according to their accepted 

 doctrines, the moon was a perfect sphere, having, of course, an entirely 

 unbroken surface. Nor would they admit that the argument from the 

 analogy of our own globe had any force. To show to what straits the 

 Aristoteleans were reduced, we may cite the attempt made by one of 

 them to reconcile the old doctrines with the new facts. Constrained 

 to admit the evidence of his senses as to the visible inequalities of the 

 lunar surface, he asserted that the observed hollows must be filled up 

 by an invisible crystalline substance, which would bring up the exterior 

 surface of our luminary to the smoothness of a perfect sphere. Galileo 

 replied that this was an admirable idea, its only fault being that it was 

 neither demonstrated nor demonstrable. " But," says he, " I am per- 

 fectly ready to believe it, provided that, with equal courtesy, you will 

 allow me to raise upon your smooth surface crystal mountains (which, 

 of course, nobody can perceive) ten times loftier than those I have seen 

 and measured." 



But when, on the yth of January, 1610, Galileo turned his telescope 

 to the planet Jupiter, a spectacle presented itself which a few sub- 

 sequent observations showed to be of still higher significance. He 

 noticed three small stars near the planet, and almost in a straight line 

 with the ecliptic. The next night he found that they appeared on 

 the other side of the planet. Plainly, therefore, either the planet had 

 moved with regard to these stars, or they had changed their positions 

 in relation to the planet. The former supposition implied that the 

 planet's motion must be in the direction contrary to that on which all 

 calculations were based. He eagerly watched for the next opportunity 

 of observing Jupiter, which was on the zoth of January, when he saw 

 two of the three stars again on the same side of the planet as on the 

 8th;- and as it was impossible to attribute to Jupiter himself movements 

 in alternate directions, he was forced to a conclusion memorable in the 

 history of astronomy, and abundantly confirmed by his subsequent 

 observations, " that there are in the heavens three stars which revolve 

 about Jupiter, in the same manner as Venus and Mercury revolve about 

 the sun." On the i3th of the same month he discovered the fourth 

 satellite. In honour of his patron, he gave the four newly-discovered 

 bodies the name of the Medicean Stars in the account which he pub-, 

 lished at the end of March, immediately after he had completed his 

 observations. These further discoveries- were a greater blow than ever 

 to the upholders of the old system. The telescopic view of the planet 

 itself presented a well-defined disc, while all the fixed stars appeared in 

 the same instrument as mere points of light, only brighter than when 



