Public ledger. [volume] (Memphis, Tenn.) 1865-1893, 1873-08-20

however, ne may De little NJ ihultl ana
for the sake Of greater accuracy, there.
fore, he will note the instant at which il
passes over all the wires" aud then
strike an average between them.
Slowly the sun creeps up TO the FIRST
line. and the observer lightly taps lit
tie spring attached 10 the telescope.
The second wire" is reached, and again
the spring is tapped, and so on through.
out the whole OF the seven or nine weiss
employed in the observation.
This spring is connected with tele-
graph wire extending to "chrono-
graph" in distant part Of the building;
and in order TO understand the method
Of recording the observation. we will now
follow the telegraphio signal, or, as
imagination is even swifter than the
telegraph, we will imagine that we have
reached the "chronograph" first, and
are there ready to receive the signals.
Accordingly we find ourselves in a
queer little chamber, in which the most
prominent object is a very beautiful
specimen Of clock, whose pendulum,
instead Of oscillating backwards and
forwards, swings round in circle, thus
producing a motion perfectly uniform
and unbroken. This clock is revolving
the cronograph," which consists Of
cylinder around which sheet Of white
paper has been strained. While we are
watching this revolving barrel we see
the observers signals come. A little
steel point which is travelling ever the
surface of the paper is in electric COM
munication with the spring attached to
the great telescope, aud every time the
observer taps the spring, this little trav-
cling point pricks into the paper, thus
recording that the sun has just crossed |
wire" This in itself, however, would |
not be record of the time Of transit il
it we're not that another little steel point,
which is in connection with galvanic |
clock in another part of the building, |
has previously marked the sheet OF paper
into spaces representing precise seconds
of time. On the completion of the OBJ.
seryation the paper may be removed
from the cylinder, and affords perma-
nent record Of it..
Nothing, perhaps, throughout the OBJ
servatory at Greenwich, is calculated to
strike the visitor with greater astonish-
ment than that galvanic clock, to which
reference has just been made. There
is nothing very remarkable in its ap-
pearance, but the work it accomplishes
renders It perhaps the most wonderful
clock in the world, and certainly the
most important one in England.
In the first place, as we have seen, it
plays an important part in registering
observations. Besides this it regulates
several clocks within the observatory,
as well as the large one already referred
to outside the gates; one at Greenwich
Hospital School, another at the London
Bridge Station of the Southeastern rail
way, another at the postoifice, st. Mar
tin sle. Grand, and another in Bombard
street. Once every day it telegraphs
correct time to the great clock tower at
Westminster it drops the signal ball
over the observatory, another near Char
ing Cross, and one at Deal; it fires time
guns at Shields and Newcastle, and
every hour throughout the day it flashes
out correct time to each of the railway
All this is accomplished as
it we're by the mere volition of the clock,
and without any human interference
whatever. Every morning it is correct
ed by an actual observation of star;
and thus, without being aware of 1t, do
we every day start our trains, aud make
our appointments, and take our meals
by the motions of the heavenly bodies as
observed and recorded during the pre-
ceding night.
We now proceed to one of those Gu
rious little domes surmounting 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 a nation of navigators, mas.
much as she affords the means of deter
mining longitude at sea. Her motions,
however, from various causes, are OF an
extremely complicated nature, and it is
very necessary that she shall be OBJ
served at all times, and under all cir
cumstances But with the transit circle,
the instrument first noticed, it is plain
that the moon could be observed only
when she is crossing the meridian, and
not always then. Some FIVE or six.and-
twenty years ago, therefore, Sir George
Airy, the present Astronomer Royal,
designed the "Altazimuth," 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
nce. 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
unar and planetary movements, as de
1eloped by theory, can be compared
With observation" Mensurative astron
lmy for practical purposes is the great
business OF Greenwich. =
The Great Equatorial telescope was y
mounted about sixteen years ago under q
he direction and from the plane of the :
present Astronomer Royal. 1t is the I
argest instrument in the Observatory,
md of its kind is one Of the finest in
he world. Its object glass, which is
hirteen inches in diameter, and has T
local distance of eighteen feet, alone
lost e4200. The most curious feature
n this telescope is the clockwork ar
-apqement By which it follows any object
lnder examination. 1t is used, as al Z
-eady intimated, chiefly for what may
1e called gazing purposes--such, for
Instance, as the scrutiny of the mar
1ellous eruptions on the surface of the q
iun, or of the mountains of the moon,
md 1t is often necessary TO con-
inue such observations for hours to-
,ether. It is plain, however, that If an n
observer is examining the face OF the
un, the motion Of the earth will gradu-
lily bear him and his telescope eastward
Until the great luminary is lost to view.
u Ii -lnnl.l-- n-.nnr. =. :. ~ : .---..-..