anetary discoveries have alternately tended to
confirm and to invalidate.

Within seventeen days of its identification with the Berlin achromatic,
Neptune was found to be attended by a satellite. This discovery was the
first notable performance of the celebrated two-foot reflector[224]
erected by Mr. Lassell at his suggestively named residence of Starfield,
near Liverpool. William Lassell was a brewer by profession, but by
inclination an astronomer. Born at Bolton in Lancashire, June 18, 1799,
he closed a life of eminent usefulness to science, October 5, 1818, thus
spanning with his well-spent years four-fifths of the momentous period
which we have undertaken to traverse. At the age of twenty-one, being
without the means to purchase, he undertook to construct telescopes, and
naturally turned his attention to the reflecting sort, as favouring
amateur efforts by the comparative simplicity of its structure. His
native ingenuity was remarkable, and was developed by the hourly
exigencies of his successive enterprises. Their uniform success
encouraged him to enlarge his aims, and in 1844 he visited Birr Castle
for the purpose of inspecting the machine used in polishing the giant
speculum of Parsonstown. In the construction of his new instrument,
however, he eventually discarded the model there obtained, and worked on
a method of his own, assisted by the supreme mechanical skill of James
Nasmyth. The result was a Newtonian of exquisite definition, with an
aperture of two, and a focal length of twenty feet, provided by a novel
artifice with the equatoreal mounting, previously regarded as available
only for refractors.

This beautiful instrument afforded to its maker, October 10, 1846, a
cursory view of a Neptunian attendant. But the planet was then
approaching the sun, and it was not until the following July that the
observation could be verified, which it was completely, first by Lassell
himself, and somewhat later by Otto Stuve and Bond of Cambridge (U.S.).
When it is considered that this remote object shines by reflecting
sunlight reduced by distance to 1/900th of the intensity with which it
illuminates our moon, the fact of its visibility, even in the most
perfect telescopes, is a somewhat surprising one. It can only, indeed,
be accounted for by attributing to it dimensions very considerable for a
body of the secondary order. It shares with the moons of Uranus the
peculiarity of retrograde motion; that is to say, its revol