In this connection attention may be called to a plan for reform in globe making proposed by Jean Dominique Cassini (1625-1712), one of the most famous astronomers of the period.[125] Cassini was a native of Périnaldo, Italy (Fig. 119). Early in life he became interested in the study of astronomy, and at the age of twenty-five received an appointment as professor of this science at the University of Bologna. Recommended by Colbert as one worthy his royal master’s patronage, Cassini in 1669 accepted the invitation of Louis XIV to fill the chair of astronomy in the Collège de France, a position once held by Pierre Gassendi.[126] In 1671 he became the director of the Royal Observatory of Paris, a position held in succession by four generations of his family. To him we owe the determination of the rotation periods of Jupiter, Venus, and Mars, the discovery of four of Saturn’s satellites and the determination of their periods of revolution. He devoted much time and study to the problem of the obliquity of the ecliptic, to the precession of the equinoxes,[127] and to the determination of the latitude and longitude of places.[128] This precession, he found, could not be represented on a celestial globe such as hitherto had been constructed, and he set himself to the task of devising one on a new plan. The position of the constellations, as indicated on the ordinary celestial globe, he, as others, noted would soon be found to be inaccurate. What he proposed was a globe capable of such adjustment as to obviate this difficulty; in other words, he proposed the construction of a globe by means of which this perpetual change might be indicated, or one which would serve to indicate the position of the several constellations at any time, past, present or future.