now universally an _entente cordiale_ that to each of these great men
belongs equally the merit of having so thoroughly calculated this
inverse problem of perturbations as to lead to the immediate discovery
of the unknown planet, since called Neptune.

It was soon found that the planet had been observed, and its position
recorded as a fixed star by Lalande, on May 8th and 10th, 1795.

Mr. Lassel, in the same year, 1846, with his two-feet reflector,
discovered a satellite, with retrograde motion, which gave the mass of
the planet about a twentieth of that of Jupiter.


FOOTNOTES:

[1] Bode's law, or something like it, had already been fore-shadowed
by Kepler and others, especially Titius (see _Monatliche
Correspondenz_, vol. vii., p. 72).




BOOK III. OBSERVATION



10. INSTRUMENTS OF PRECISION--STATE OF THE SOLAR SYSTEM.


Having now traced the progress of physical astronomy up to the time