The observations which he made upon the moon possessed a high degree of interest. The general resemblance of its surface to that of our own globe naturally fixed his attention; and he was soon able to trace, in almost every part of the lunar disc, ranges of mountains, deep hollows, and other inequalities, which reflected from their summits the rays of the rising sun, while the intervening hollows were still buried in darkness. The dark and luminous spaces he regarded as indicating seas and continents, which reflected, in different degrees, the incident light of the sun; and he ascribed the phosphorescence, as it has been improperly called, or the secondary light, which is seen on the dark limb of the moon in her first and last quarters, to the reflection of the sun's light from the earth. These discoveries were ill received by the followers of Aristotle. According to their preconceived opinions, the moon was perfectly spherical, and perfectly smooth; to cover it with mountains, and to scoop it out into valleys, was an act of impiety which defaced the regular forms which nature herself had imprinted. It was in vain that Galileo appealed to the evidence of observation, and to the actual surface of our own globe. The very irregularities on the moon were, in his opinion, the proof of divine wisdom: and had its surface been perfectly smooth, it would have been "but a vast unblessed desert, void of animals, of plants, of cities, and of men; the abode of silence and inaction; senseless, lifeless, soulless, and stripped of all those ornaments which now render it so various and so beautiful." In examining the fixed stars, and comparing them with the planets, Galileo discovered a remarkable difference in the appearance of their discs. All the planets appeared with round globular discs like the moon; whereas the fixed stars never exhibited any disc at all, but resembled lucid points sending forth twinkling rays. Stars of all magnitudes he found to have the same appearance; those of the fifth and sixth magnitude having the same character when seen through a telescope, as Sirius, the largest of the stars, when seen by the naked eye. Upon directing his telescope to nebulæ and clusters of stars, he was delighted to find that they consisted of great numbers of stars which could not be recognised by unassisted vision. He counted no fewer than _forty_ in the cluster called the _Pleiades_, or _Seven Stars_; and he has given us drawings of this constellation, as well as of the belt and sword of Orion, and of the nebula of Præsepe. In the great nebula of the Milky Way, he descried crowds of minute stars; and he concluded that this singular portion derived its whiteness from still smaller stars, which his telescope was unable to separate.