By De la Rue's advice, Pritchard began his career there with a determination of the physical libration of the moon, or the nutation of its axis.
He reverted to his early idea of a nutation of the earth's axis, and was rewarded by the discovery that the earth did possess such an oscillation (see Astronomy).
At the same time the frictional drag damps the nutation and causes the axis of the shot to follow the tangent of the trajectory very closely, the point of the shot being seen to be slightly above and to the right of the tangent, with a right-handed twist.
This star was seen to possess an apparent motion similar to that which would be a consequence of the nutation of the earth's axis; but since its declination varied only one half as much as in the case of y Draconis, it was obvious that nutation did not supply the requisite solution.
In 1749 he furnished a method of applying his principles to the motion of any body of a given figure; and in 1754 he solved the problem of the precession of the equinoxes, determined its quantity and explained the phenomenon of the nutation of the earth's axis.
He refrained from announcing the supplementary detection of nutation until the 14th of February 1748 (Phil.
Bradley, was the first to represent the effects of nutation in the solar tables, and introduced, in 1741, the use of the transitinstrument at the Paris observatory.