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HISTORICAL VIEW OF THE

analogous case of a ball dropped from the mast-head ofa ship in motion, and of a body thrown across the deck,were referred to; and it was contended, they, in likemanner, would fall behind. This was admitted by theCopernicans , because, as they said, these bodies werenot part of the ship.

The true way of answering was not attempted;namely, by trying the experiment. The real replywould have been, that the ball does fall precisely at thefoot of the mast; and the body thrown strikes exactlythe opposite point of the deck. In the case of a bodydropped from a tower, there would, indeed, be an inap-preciable deviation, owing to the velocity of the top ofthe tower being slightly greater than that of the surfaceof the earth ; in the ratio of the height of the tower, tothe radius of the globe. But, abstracting from this, thebody falls at the foot of the tower. Galileo also showedthat bodies thus in motion partake in the motion of themass to which they belong, not by virtue of any suchmetaphysical principles as those referred to by theAristotelians, but from mechanical causes dependenton the communication of motion.

The physical difficulties being disposed of, it remainedonly to compare the respective systems in an astronomi-cal point of view. And here the advantage of the Co-pernican is palpable and immense. Its simplicity anduniformity is admirably and convincingly contrastedwith the complexity of the Ptolemaic hypothesis, andthe inconceivably difficult suppositions which the latterinvolves as to the velocity with which the heavenlybodies must move. Indeed, the Ptolemaists themselveswere constrained to admit the superiority of Copernicus in this respect: they held out, not on these grounds,but on the physical objections drawn from the Aris-totelian doctrine, and the decrees of the church.

( On the subject of the tides Galileo is less happy. Hesuggests, indeed, a theory, but of a very unsatisfactorynature. The college of Jesuits at Coimbra appear tohave first given a hint of the real cause in their com-