ome of the sun's metals do not appear. Stars differ in their very
substance, and will, no doubt, introduce new elements to us unknown
before.

The theory that all nebulae are very distant clusters of stars is
utterly disproved by the clearest proof that some of them are only
incandescent gases of one or two kinds.

_Discoveries of New Bodies._--Vulcan, the planet nearest the sun
(page 138). The two satellites of Mars were discovered by Mr. Hall,
U. S. Naval Observatory, August 11th, 1877 (page 161). "The outer
one is called Diemas; the inner, Phobus.

Sir William Herschel thought he discovered six satellites of Uranus.
The existence of four of them has been disproved by the researches of
men with larger telescopes. Two new ones, however, were discovered
by Mr. Lassell in 1846.

_Saturn's Rings_ are proved to be in a state of fluidity and contraction
(page 171).

_Meteors and Comets._--The orbits of over one hundred swarms of
meteoric bodies are fixed: their relation to, and in some cases
indentity with, comets determined. Some comets are proved to be
masses of great weight and solidity (page 133).

_Aerolites._-Some have a texture like our lowest strata of rocks.
There is a geology of stars and meteors as well as of the earth. M.
Meunier has just received the Lalande Medal from the Paris Academy
for his treatise showing that, so far as our present knowledge can
determine, some of these meteors once belonged to a globe developed
in true geological epochs, and which has been separated into fragments
by agencies with which we are not acquainted.

[Illustration: Fig. 82.--Horizontal Pendulum.]

_The Horizontal Pendulum._--This delicate instrument is [Page 272]
represented in Fig. 82. It consists of an upright standard, strongly
braced; a weight, _m_, suspended by the hair-spring of a watch, B D,
and held in a horizontal position by another watch-spring, A C. The
weight is deflected from side to side by the slightest influence.
The least change in the level of a base thirty-nine inches long that
could be detected by a spirit-level is 0".1 of an arc--equal to
raising one end 1/2068 of an inch. But the pendulum detects a
raising of one end 1/36000000 of an inch. To observe the movements
of the pendulum, it is kept in a dark room, and a ray of light is
directed to the mirror, _m_, and thence reflected upon a screen.
Thus the least movement may be enormously magnified, and read and
measured by the moving spot on the s