tions 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 HERSCHEL 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 perceived one that
appeared visibly larger than the rest; being struck with its uncommon
appearance, I compared it to H _Geminorum_ and the small star in the
quartile between _Auriga_ and _Gemini_, and finding it so much larger
than either of them, I suspected it to be a comet." The "comet" was
observed over all Europe. Its orbit was computed by various astronomers,
and its distance from the sun was found to be nineteen times that of our
earth. This was no comet, but a new major planet. The discovery of the
amateur astronomer of Bath was the most striking since the invention of
the telescope. It had absolutely no parallel, for every other major
planet had been known from time immemorial.[13]

The effect of the discoveries of GALILEO was felt almost more in the
moral than in the scientific world. The mystic number of the planets was
broken up by the introduction of four satellites to _Jupiter_. That
_Venus_ emulated the phases of our moon, overthrew superstition and
seated the Copernican theory firmly. The discovery of "an innumerable
multitude of fixed stars" in the Milky Way confounded the received
ideas. This was the great mission of the telescope in GALILEO'S hands.

The epoch of mere astronomical discovery began with the detection of the
large satellite of _Saturn_ by HUYGHENS, in 1655. Even then superstition
was not dead. HUYGHENS did not search for more moons, because by that
discovery he had raised the number of known satellites to six,[14] and
because these, with the six planets, made "the perfect number twelve."

From 1671