ver, effected
the important improvement of measuring the decline of light of the
satellite undergoing eclipse by the photometer. Much additional
precision may be anticipated in the results of such observations.

[24] "Newcomb's Popular Astronomy," p. 336.

[25] _See_ Grant, "History of Physical Astronomy," page 255.

[26] Now Director of the Lick Observatory.

[27] We are here neglecting the orbital motion of Saturn, by which the
whole system is moved towards or from the earth, but as this motion is
common to the ball and the ring, it will not disturb the relative
positions of the three spectra.

[28] According to Prof. Barnard's recent measures, the diameter of Titan
is 2,700 miles. This is the satellite discovered by Huyghens; it is the
sixth in order from the planet.

[29] Extract from "Three Cities of Russia," by C. Piazzi Smyth, vol.
ii., p. 164: "In the year 1796. It then chanced that George III., of
Great Britain, was pleased to send as a present to the Empress Catharine
of Russia a ten-foot reflecting telescope constructed by Sir William
Herschel. Her Majesty immediately desired to try its powers, and
Roumovsky was sent for from the Academy to repair to Tsarskoe-Selo,
where the Court was at the time residing. The telescope was accordingly
unpacked, and for eight long consecutive evenings the Empress employed
herself ardently in observing the moon, planets, and stars; and more
than this, in inquiring into the state of astronomy in her dominions.
Then it was that Roumovsky set before the Imperial view the Academy's
idea of removing their observatory, detailing the necessity for, and the
advantages of, such a proceeding. Graciously did the 'Semiramis of the
North,' the 'Polar Star,' enter into all these particulars, and warmly
approve of the project; but death closed her career within a few weeks
after, and prevented her execution of the design."

[30] _See_ Professor Holden's "Sir William Herschel, his Life and
Works."

[31] Arago says that "Lemonnier's records were the image of chaos."
Bouvard showed to Arago one of the observations of Uranus which was
written on a paper bag that in its time had contained hair-powder.

[32] The first comet of 1884 also suddenly increased in brightness,
while a distinct disc, which hitherto had formed the nucleus, became
transformed into a fine point of light.

[33] The three numbers 12, 1, and 1/4 are nearly inversely proportional
to the atomic weights of hydrogen, hy