morality?” The discovery of the great nebula in Orion was accidentally made by Huygens in the year 1656. Cassini, nurtured in France, soon afterward added four more satellites to the system of Saturn, those now called the first, second, third, and fifth, and he detected the black list, or dark, elliptical line bisecting the surface of the ring, and dividing it into two. Astronomy is under immense obligations to a measure adopted by the courts of France and England at nearly the same period, for the patronage of scientific associations, and the founding of national observatories. The Royal Society of London was incorporated by charter in the year 1662, and numbered among its early members Boyle, Hooke, Wallis, Ward, Newton, and Flamstead. The Royal Academy of Sciences at Paris, was founded in the year 1666, and enrolled among its first members Auzout, Picard, Roberval, and Richer. Upon the invitation of Louis XIV. Huygens left Holland to become a royal academician, but being a Protestant, the revocation of the edict of Nantes ultimately compelled him to return to his native soil. The edict did not affect Cassini, a Catholic foreigner similarly invited; and to him, with his son and grandson, the French academy owes much of its early distinction. Besides his before named discoveries, he determined the periods of rotation of the principal planets, and observed the elliptical form of Jupiter’s disc, owing to compression at the poles. Roëmer, the inventor of the transit instrument with which he made observations from the window of his house, rendered no unimportant service by showing that the instruments need not be fixed on high towers: he also discovered, in the year 1675, the interesting and hitherto unsuspected fact, of the progressive transmission of light through space, and the appreciable velocity with which it travels. This was attained by a series of careful observations of the eclipses of Jupiter’s satellites. It was found, by comparing the times of immersion of the satellites in the planet’s shadow and emersion from it, with the times calculated from the laws of their movements, that there was an acceleration or retardation of the phenomena by a few minutes, plainly dependent upon the variations of the earth’s distance from Jupiter; for [Illustration]