Page:Sir William Herschel, his life and works (1881).djvu/70

48 when he said: "A knowledge of the construction of the heavens has always been the ultimate object of my observations."

The title of this paper was Astronomical Observations on the Rotation of the Planets round their Axes, made with a view to determine whether the Earth's diurnal motion is perfectly equable. Here the question is a difficult and a remote one, and the method adopted for its solution is perfectly suitable in principle. It marks a step onward from mere observations to philosophizing upon their results. In practical astronomy, too, we note an advance. Not only are his results given, but also careful estimates of the errors to be feared in them, and a discussion of the sources of such errors. The same volume of the Philosophical Transactions which contains this paper, also contains another, Account of a Comet, read April 26, 1781. This comet was the major planet Uranus, or, as named it, Georgium Sidus. He had found it on the night of Tuesday, March 13, 1781. "In examining the small stars in the neighborhood of H Geminorum, I