creen. It has been discovered
that when the sun rises it has sufficient attraction to incline this
instrument to the east; when it sets, to incline it to the west. The
same is true of the moon. When either is exactly overhead or
underfoot, of course there is no deflection. The mean deflection
caused by the moon at rising or setting is 0".0174; by the sun,
0".008. Great results are expected from this instrument hardly known
as yet: among others, whether gravitation acts instantly or consumes
time in coming from the sun. This will be shown by the time of the
change of the pendulum from east to west when the sun reaches the
zenith, and _vice versa_ when it crosses the nadir. The sun will be
best studied without light, in the quiet and darkness of some deep
mine.

[Page 273]
_Light of Unseen Stars._--From careful examination, it appears
that three-fourths of the light on a fine starlight night comes
from stars that cannot be discerned by the naked eye. The whole
amount of star light is about one-eightieth of that of the full
moon.

_Lateral Movements of Stars_, page 226-28.

_Future Discoveries_--_A Trans-Neptunian Planet._--Professor Asaph
Hall says: "It is known to me that at least two American astronomers,
armed with powerful telescopes, have been searching quite recently for
a trans-Neptunian planet. These searches have been caused by the fact
that Professor Newcomb's tables of Uranus and Neptune already begin
to differ from observation. But are we to infer from these errors of
the planetary tables the existence of a trans-Neptunian planet? It
is possible that such a planet may exist, but the probability is, I
think, that the differences are caused by errors in the theories of
these planets. * * * A few years ago the remark was frequently made
that the labors of astronomers on the solar system were finished, and
that henceforth they could turn their whole attention to sidereal
astronomy. But to-day we have the lunar theory in a very discouraging
condition, and the theories of Mercury, Jupiter, Saturn, Uranus,
and Neptune all in need of revision; unless, indeed, Leverrier's
theories of the last two planets shall stand the test of observation.
But, after all, such a condition of things is only the natural
result of long and accurate series of observations, which make
evident the small inequalities in the motions, and bring to light
the errors of theory."

Future discoveries will mostly reveal the laws and condition