"The same effect which the Sun produces upon the Earth by its attraction, it also produced by the Moon which acts with greater force in proportion as it is more distant from the equator: Now, at the time when its nodes concur with the equinoxial points, its greatest latitude is added to the greatest obliquity of the ecliptic. At this time, therefore, the power which causes the irregularity in the position of the terrestrial axis, acts with the greatest force; and the revolution of the nodes of the Moon, being performed in eighteen years, it is clear, that in eighteen years the nodes will twice concur with the equinoxial points; and, consequently, that twice in that period, or once every nine years, the Earth's axis will be more influenced than at any other time; so that it will have a kind of balancing backward and forward, the period of which will he nine years, as Mr. Bradley had observed; and this ballancing he called the Nutation of the Terrestrial Axis. He published this discovery in 1737, so that in the space of about ten years he communicated to the world two of the finest discoveries in modern astronomy, which will for ever make a memorable epocha in the history of that science."