running across the brighter ground on which the
expected star is to be visible.

The adjustment of the instruments is a task
of great nicety. If they are out of trim only
a shadow of a shade of a hair's-breadth, the
desired accuracy is interfered with, and they
have to be re-adjusted. Temperature is of
course an important element in their
condition, and a slight sensibility may do
mischief. The warmth of the observer's body,
when approaching the instruments, has been
known to affect their accuracy; and to avoid
such sources of error, instruments have at
times been cased in flannel, that the non-
conducting powers of that homely fabric might
screen the too-sensitive metal.

Sunday is a comparative holiday at the
Observatory, for then, except when any extra-
ordinary phenomena are expected, the only
duty done is to drop the Time Ball, and observe
the moon's place. The moon is never neglected,
and her motions have been here watched,
during the last hundred and seventy years,
with the most pertinacious care,-- to the great
service of astronomy, and the great benefit of
navigation.

The library should not pass unnoticed. It
is small; but being devoted to works upon
astronomy, and the kindred sciences, there is
ample room for all that has hitherto been
written on the subject, or that can, for many
generations, be produced. The observations
of a lifetime spent in watching the stars may
be printed in marvellously few pages. A
glance through the Greenwich Astronomical
Library gives a rough general idea of what
the world has done and is doing for the
promotion of this science. Russia contributes
large, imperial-looking tomes, that tell of
extended observations made under the
munificent patronage of a despot; Germany sends
from different points a variety of smaller,
cheaper-looking, yet valuable contributions;
France gives proofs of her genius and her
discoveries; but her forte is not in observation.
The French are bad observers. They
have no such proofs of unremitting, patient
toil in search of facts, as those afforded in
the records of the Greenwich Tables of the
Moon. Indeed, Greenwich, as we have already
said, is a working Observatory; and
those who go into its library, and its fire-proof
manuscript-room, and see how its volumes
of observations have been growing from the
small beginnings of the days of Flamstead
and Halley, to those of our later and more
liberal times, will have good reason to
acknowledge that the money devoted to this
establishment has been well employed.

One other spot must be noticed as amongst
the notable things in this astronomical sanctum.
It is the Chronometer-room, to which,
during the first three Mondays in the year, the
chief watchmakers of London send in their
choicest instruments for examination and trial.
The watches remain for a good portion of a
year; their rates being noted, day by day, by
two persons; and then the makers of the best
receive prizes, and their instruments are purchased
for the navy. Other competitors obtain
certificates of excellence, which bring customers
from the merchant service; whilst
others pass unrewarded. To enter the room
where these admirable instruments are kept,
suggests the idea of going into a Brobdingnag
Watch-factory. Round the place are ranged
shelves, on which the large watches are placed,
all ticking in the most distinct and formidable
way one against another. When they first
arrive, in January, they are left to the ordinary
atmospheric temperature for some
months. Their rates being taken under these
circumstances, a large stove in the centre of
the apartment is lighted, and heat got up to
a sort of artificial East India or Gold Coast
point. Tried under these influences, they are
placed in an iron tray over the stove, like so
many watch-pies in a baker's dish, and the
fire being encouraged, they are literally kept
baking, to see how their metal will stand that
style of treatment. Whilst thus hot, their
rates are once more taken; and then, after
this fiery ordeal, such of them as their owners
like to trust to an opposite test, are put into
freezing mixtures! Yet, so beautifully made
are these triumphs of human ingenuity-- so
well is their mechanism ' corrected ' for
compensating the expansion caused by the heat,
and the contraction induced by the cold--
that an even rate of going is established, so
nearly, that its variation under opposite
circumstances becomes a matter of close and
certain estimate.

The rates of chronometers on trial for
purchase by the Board of Admiralty, at the
Observatory, are posted up and printed in an
official form. Upon looking to the document
for last year, we find a statement of their
performances during six months of 1849, with
memoranda of the exact weeks during which
the chronometers were exposed to the open
air at a north window; the weeks the
Chronometer-room was heated by a stove, the
chronometers being dispersed on the
surrounding shelves; and the weeks during
which they were placed in the tray above
the stove. The rate given during the first
week of trial is in every case omitted;
like newly entered schoolboys their early
vagaries are not taken into account; but
after that, every merit and every fault is
watched with jealous care, and, when the
day of judgment comes, the order of the
arrangement of the chronometers in the list
is determined solely by consideration of their
irregularities of rate as expressed in the
columns, 'Difference between greatest and
least,' and, 'Greatest difference between one
week and the next.'

The Royal Observatory, according to a
superstition not wholly extinct, is the head-
quarters, not only of Astronomy, but of Astrology.
The structure is awfully regarded, by
a small section of the community which