American citizen. [volume] (Canton, Miss.) 1864-1890, 1873-08-30

Schools, another at the London Bridge
Station of the South Eastern Railway,
another at the Post Office, ST. Martin's-le-
Grand, and another in Lombard Street.
| Once every day it telegraphs correct
time to the great clock tower at West
minister; it drops the signal ball over the
| Observatory, another near Charing Cross,
and one ut Deal it fires time guns at
Shields and Newcastle, and every hour
J throughout the day it flashes out correct
| time to each of the railway companies.
All this is accomplished as it were by
| the mere volition of the clock, and with
out any human interference whatever.
Every morning it is corrected by an actual
observation of star; and thus, without
| being aware of it, do we every day start
our trains, and make our appointments,
and take our meals by the motions of the
heavenly bodies as observed and recorded
during the preceding night.
We now proceed to one of those curl
Gus little domes surrounding various
parts of the Observatory. Here we find
an instrument devoted entirely to the
study of the moon Observations of the
moon are of immense importance to us
as nation of navigators, inasmuch as
she affords the means of determining
longitude at sea. Her motions however,
from various causes, are of an extremely
complicated nature, and it is very neces-
sary that she shall be observed at all
times, and under all circumstances. But
with the transit circle, the instrument
first noticed, it is plain that the moon
could be observed only when she is cross
ing the meridian, and not always then.
Some five or six-and-twenty years ago,
therefore, Sir George Airy, the present
Astronomer Royal, designed the "AltaZi-
muth," and since then the importance of
Greenwich as lunar observatory has
been just about doubled.
With this instrument and the transit
circle the Observatory might do all that,
strictly speaking, comes within its prov
ince. The whole duty of Greenwich, as
defined by Herschel, is 'to furnish now,
and in all future time, the best and most
perfect data by which the laws of the
lunar and planetary movements, as de-
veloped by theory, can be compared with
observation" Mensurative astronomy
for practical purposes is the great bust
ness of Greenwich.
The Great Equatorial telescope was
mounted about sixteen years ago, under
the direction and from the plans of the
present Astronomer Royal. 1t is the
largest instrument in the Observatory,
and of its kind is one of the finest in the
world. Its object glass, which is thirteen
inches in diameter, and has a focal dis
lance of eighteen feet, alone cost 81, 200.
The most curious feature in this telescope
is the clOckwOrk arrangement by which
it follows any object under examination.
1t is used, as already intimated, chiefly
for what may be called gazing purposes
such, for instance, as the scrutiny of the |
marvellous eruptiOns on the surface of the
sun, or of the mountains of the moon, and
it is often necessary to continue such OBJ
servations for hours together. 1t is plain, |
however, that if an observer is examining
the face of the sun, the motion of the
earth will gradually bear him and his
telescope eastward until the great lumin-
ary is lost to view. He will steadily
creep out at the western side of the field. |
This is obviated by the operation of a
powerful piece of mechanism is connect |
ed with the great iron framework support |
ing the telescope, and just as the earth |
creeps round from west to east, the tele- |
scope and all that pertains to it is borne |
round from east to west. Thus, so far as |
the motion of the earth is concerned, the |
sun, moon, or stars as seen through the |
fectly stationary.
We have now seen all the more prOmi- |
nent features of Greenwich Observatory, |
though there yet remain innumerable OBJ |
jects of the utmost interest-rain guages, |
hygrometers, and ther-
placed in all kinds of posi- |
tons, and under all kinds of conditions. |
In one room are something like couple |
of hundred Government chronometers, |
placed here for the purpose of being |
regulated, while in building apart from
The Astronomical Observatory is a Mag
netic Observatory, established for the |
purpose of ascertaining and recording |
The various phenomena of the magnetic |
currents of the earth.-Cdsselps Magazine.