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HISTORICAL VIEW OP THE

great system of the planetary orbits. It was basedupon the only kind of argument which could in thatage have been adduced ; viz. that it completely ex.plained the phenomena which observation had revealed,and that it did so with infinitely greater simplicity thanany hypothesis hitherto proposed. The objections whichhad been brought against it on the grounds of the Aris-totelian physics were completely answered, and it waseven defended on principles which its opponents of thatschool would be the last to call in question.

Copernicus had himself been assiduous in makingobservations, and we learn from his commentator,Rhfeticus, that what first led him to entertain the Py-thagorean doctrine, was, that his observations on theplanet Mars showed him distinctly the very consider-able difference in the apparent magnitudes of thatplanet at different times, whence he inferred the relativeposition of the orbits of Mars and of the earth; hemade also this remarkable observation, — that if the senseof sight could ever be rendered sufficiently powerful, weshould see phases in Mercury and Venus.

Copernicus was sufficiently cautious in the promul-gation of his system, being fully aware of the pre-judices he had to encounter. In the first instance hisviews were only made known through the channel ofprivate correspondence and friendly conversation. Thushis contemporaries found nothing to startle their pre-possessions, or to provoke hostility. Opinions eman-ating from one of their own body excited no jealousyamong the ecclesiastics: and several prelates were evenurgent with Copernicus to publish his researches. Atlength his disciple Rlneticus printed, in 1540, “AnAccount of a Manuscript of Copernicus .” This beingreceived with approbation, the author himself wasprevailed upon to proceed with the publication of hisown work, which he dedicated to the pope, in order,as he says, that'the authority of the head of the churchmight silence the calumnies of individuals who attackedhis views by arguments drawn from religion.