certainly known is probably very much less than we imagine. A
great deal that was received as certain a few years ago, is now
considered to be doubtful, or even recognized as a mistake and
abandoned. This is especially the case with Astronomy, which seems
to be almost in a state of revolution. Dependent, as it is almost
entirely, upon mechanical and optical aid, every improvement and
discovery in these departments changes its position, bringing to
light new facts, and modifying the aspect of those which were
previously known. The very basis of all astronomical calculations,
the standard of time, is now no longer relied upon as invariable.
It is suspected of a change resulting from a gradual retardation
in the rate of the earth's rotation on its axis, produced by tidal
friction. When the binary stars were discovered, the discovery was
hailed as a proof of the universal prevalence of the law of
gravitation. Later observations have thrown doubt upon that
conclusion, as many pairs are known to exist, which, though they
have what is termed a "common proper motion," or are journeying
through space together, have no relative motion, which they must
show, if they were moving under the influence of their mutual
attractions. The supposed simplicity of the solar system has given
place to extreme complexity. A century ago, six planets, ten
satellites, and a few comets, were supposed to constitute the
whole retinue of the sun: now, instead of this, we have two groups
of four planets each, the individual members of each group closely
resembling each other in all points within our knowledge, while in
all these points the groups differ greatly. Between these two
groups lies a belt of very small planets, of which the 1st was
discovered on the first day of the present century, and the 124th
this year, and the number of known satellites has increased from
10 to 17. Add to this the meteoric groups, and their suspected