The Sun.
London, England, 1854-10-27 00:00:00

THE ASTEONOMER ROYAL IN A COAL

PIT.

NEWCASTLII, Oct. 25.—The Astronomer Royal, Pro
feseor Airey, has been engaged in the North during the
past three weeks pursuing a series of interesting and
delicate experiments, with a view of determining some
important questions with regard to the density of the
earth. The learned savan has been assisted in his im-
portant investigations by a staff of assistants from dif-
ferent observatories in the kingdom.
Mr. Dunkin, of the Royal Observatory, Greenwich,.
who, in the absence of the Astronomer Royal, had charge
of the experiments ; Mr. Ellis, also of the Royal Obser-
vatory ; Mr. Pogson, of the Redcliffe Observatory, Ox-
ford ; Mr. Rumker, of Durham Observatory ; Mr. Cris-
wick, of Cambridge Observatory ; and Mr. Simmonds,
of Mr. Carrington 's private observatory, Red-hill, Sur-
rey, have been engaged making daily ebservations.
Horton Colliery, which was the scene of these im-
portant observations, is about two miles south of South
Shields, and is well adapted for the purpose, being one
of the deepest coal mines in the neighbourhood. The
lowsr station was 1,260 feet below the surface of the
earth. The observations consisted in noting the vibra-
tions of an invariable pendulum on the surface, and
another at the bottom of the mine, both being mounted
on iron stands similar to each other. These pen-
dulums hang on knife edges, resting on agate planes,
thus sustaining little resistance from friction. If swung
in vacuo, the vibrations would probably have continued
for Swenty-four hours, and in their state as used, though
liable to hindrance from atmospheric causes, yet the
• vibrations continued at least eight ar nine hours. Cor-
rections were applied to the results from the effects of
temperature, and also for buoyancy, or the effect pro-
duced by the pressure of the air on the pendulum. The
vibrations were counted by the assistance of a clock,
which was mounted immediately behind the detached
pendulum ; and thus, by the aid of the clock, the number
of vibrations in a certain time could be easily noted.
The method was simply this ;—To the centre of the bola
of the clock pendulum was attached a small oval-shaped
disc, covered with gold leaf, and illuminated by
a lamp.
It was necessary in the adjustments that this disc, when
and stationary,that tshheorueldshboeuldhibde bya th,,ltttitd,entactliiieed c
cn
kdhere-
ucl na
sme
which should also be just covered by it. A line, t
here-
fore, fore, drawl through the centre of the telescope, w
was placed at a little distance through the detached
pendulum, the slit in the clock case, acid the Wilma
nated disc on the clock pendulum should be a straight
lino: Suppose the two pendulums wore set swinging,
we should then perceive that one was vibrating faster
than the other, and that the disc would he gradually
approaching the detached pendulum until it would
be completely hid, and both pendulums would be
going exactly together. This was called a coincidence,
and wits carefully noted to the nearest second of
time. When the illuminated disc reappeared, which was
generally in a few sec-made, one pendulum still continued
gaining on the other, until another coincidence took
place, the time was again noted, and thus we have the
interval of coincidence, or the time occupied in one pen-
dulum gaining two seconds over the other. The rate of
one pendulum was easily found ; and as this operation
Was performed simultaneously at the upper andlower
stations, nothing remained but the comparison of the two
clocks. In the Astronomer Royal's former effperiments
in Cornwall this was the most difficult part of tho
opera-
tion. It that time it was necessary to fasten the clasono-
meters to the body by means of straps, and ther to
as-
cend or descend by perpendicular ladders, a journey
which occupied considerably more than an hour in its
accomplishment. In the present experiment this section
of the observations was qnite, if not more satisfactory
than the observation of coincidences, owing to the adap-
tation of galvanism to astronoraleal purposes, and by
this means the comparison of the clocks was effected. A
wire coated with gotta percha passed from one pole of the
battery through aclock, which was so arranged as to push
a spring, causing a galvanic circuit every 15seeonds, from
the clock the wire passed through a galvanometer at-
tached to the clockcase at the upper station, thence un-
derground to the shaft, down which it descended to the
lower station, when it passed through another galvano-
meter also attached to the lower clockcase, it then re-
turned up the shaft to the other pole‘of the battery, and
thus the circuit was completed. Signals were simultaxe-
ously observed by the observer at the upper and lower
stations, which gave a direct comparison of the two
clocks. By this means every element for the determination
of the gain or loss of the tipper pendulum over the lower,
and consequently the difference of the force of gravity
acting on both pendulums, was formed by calculation.
The observations extended over a period of three weeks,
the pendulums remaining the first week in the same posi-
tion. In the second week they were reversed, so as to elimi-
nate any error which may attach to either pendulum.
In the third week they were reversed in the middn of
the week. No result has yet been obtained, as tha dis-
t mission of the large mass of observations will require
anasiderable time and attention, but cnoagh has been
done to show that the observations are of a very superior
I character, and it is the Astronomer Royal's opinion that
most valuable results will be obtained from theta.