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HISTORY OF PHYSICAL ASTRONOMY.
first saw tliem. They were all now on the west side of the planet, and
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were nearer to each other than they had been on the previous evening;they were also disposed at equal distances from each other. The strangefact of the mutual approach of the stars did not yet strike his attention,but it excited his astonishment, that Jupiter should be seen to the east ofthem all, when only the preceding night he had been seen to the west oftwo of them. He was induced, on this account, to suspect that themotion of the planet might be direct, contrary to the calculations ofastronomers, and that he had got in advance of the stars by means of hisproper motion. He therefore waited for the following night with greatanxiety, but his hopes were disappointed, for the heavens were on allsides enveloped in clouds. On the 10th he saw only two stars, and theywere both on the east side of Jupiter . He suspected that the third
might be concealed behind the disc of the planet. They appeared asbefore in the same right line with him, and lay in the direction of thezodiac. Unable to account for such changes by the motion of the planet,and being at the same time fully assured that he always observed thesame stars, his doubts now resolved themselves into admiration, and hefound that the apparent motions should be referred to the stars them-selves and not to the planet. He therefore deemed it an object ofparamount importance to watch them with increased attention.
On the 11th he again saw only two stars, and they were also both onthe east
side of Jupiter . The more eastern one appeared nearly twice as large asthe other, although on the previous evening he had found them almostequal. This fact, when considered in connexion with the constant changeof the relative positions of the stars and the total disappearance of oneof them, left no doubt on his mind of their real character. He thereforecame to the conclusion, that there are in the heavens three stars revolvinground Jupiter in the same manner as Venus and Mercury revolve roundthe sun. On the 12tli he saw three stars; two on the east side of