The Sun.
London, England, 1851-03-20 00:00:00

THURSDAY EVENING, MARCH 20, 1851.

SOCIETY OF ARTS.

At the fifteenth ordinary meeting of the Society,
held last evening, the discussion on Mr. Hay's paper
on the "Beautiful" was resumed. Mr. Joseph Jop-
ling then read a paper on "Practical Geometric
Curves," and his recent discoveries in reference to
curved sections of cones. In the last report of the
proceedings of the Society, a detailed account is
given of the electro-magnetic clock which, by per-
mission of the Royal Commissioners for the Great
Exhibition, is to be fixed on the transept of the
Crystal Palace. It has been proposed by Mr. Owen
Jones that the figures should be arranged in a semi-
circle, because a circular dial would greatly interfere
with the design of the building. This proposal was
accordingly adopted, the figures being placed on spaces
left at the intersection of the second semicircular rib
from the centre, with the radial bars of the south end
of the transept.
In order to indicate the time on a semicircular dial
throughout the twenty-four hours, it was necessary
that the hands should be double, projecting equally
on both sides of the centre. The minute-hand revolves
once in two hours ; and as one end leaves the right
side of the dial at six o'clock, the opposite end com-
mences at six on the left. The minute-haud is six-
teen feet long, and the hour-hand twelve.
The framing of the clock for moving the hands of
this large dial is of cast-iron, gun• metal bushes being
let in to receive the pivots. There aro two wheels
between the frames, one large wheel 18 inches in
diameter, with 240 teeth, and the escape-wheel, with
120 ratchet teeth. This wheel is in two parts, the
teeth of each part being arranged in contrary direc-
tions ; a click falls into each of these sets of teeth,
one preventing the wheel from running back when
moving forward, the other preventing it from moving
forward by the action of the wind upon the hands.
When the escape-wheel is to be moved forwards,
which in this clock is every two seconds, this click
must first be raised, which is effected by a pin pro-
jecting from the motive click, actuated by the electro-
magnet. The stopping click being raised, the motive
click, as it advances, carries the wheel forward;
before it has advanced the wheel to the full extent,
the pin in the motive-click is disengaged from the
stopping-click ; the latter being dropped into its
wheel, stops all further motion until again raised by
the motive• click at the next action.

The arbor of the large wheel projects through the
frame, and carries a vertical bevelled wheel twelve
inches in diameter. This wheel takes into the teeth
of a horizontal bevelled wheel of the same size ; from
the arbor of this wheel the motion is to be carried up
to the hands by a rod composed of lengths of brass
tubing screwed together. There will be eight electro-
magnets, composed of charcoal-iron, three quarters
of an inch square ; on each leg of the magnets is
placed's brass reel, carrying more than 1,500 feet of
copper-wire, or 25,000 feet in all, the weight of which
is about 1 cwt.
This clock, although quite equal to that at St.
Paul's Cathedral, occupies far less space, the heavy
weights, with the room necessary for their descent,
being of course dispensed with. Besides this large
dial in the transept, there are to be two smaller ones,
five feet in diameter each : one of these dials will be
placed in front of the galleries at each end of the
building. The whole three will be regulated by one
pendulum.