FOR DETERAJINING THE MEAN DENSITY OF THE EARTH. 
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tbe coal-trams, &c. on the tram-way was inaudible. The Harton shaft is the dovvn- 
cast air-shaft for a very extensive series of workings, of which the upcast shaft is at 
the St. Hilda pit in the town of South Shields ; and the lower pendulum station, from 
its proximity to the Harton pit, was constantly and agreeably ventilated with pure 
fresh air. 
The owners of the mine immediately proceeded, at their own expense, to make the 
following preparations for the pendulums. 
11. In the stable for the upper station, an additional brick wall was built round 
three sides of the space (about 16 feet square) intended for the pendulum room, and 
an additional substantial ceiling was constructed above it ; and an anteroom was 
constructed on the fourth side ; so that the room was in fact surrounded by double 
walls and ceiling. The immediate entrance from the external air was into the ante- 
room ; and from the anteroom there were doors into the pendulum room and into a 
narrow room at one side. [In this narrow room were afterwards placed the galvanic 
batteries and journeyman-clock, and the lamp for illuminating the pendulum disk. 
The lamp for illuminating the face of the principal clock was in the anteroom, giving 
its light through a hole in the dividing wall ; and the observer was stationed in the 
anteroom, his observing telescope being fixed in a hole in the wall.] From the 
gas-works of the mine, gas was led to a gas-stove in the anteroom, and also to a 
writing-lamp. In order to make the support of the pendulum firm, the soft earth 
was removed to the depth of 3 feet (at which level the hard clay was reached, which 
extends about 90 feet lower to the first bed of rock), and the cavity was filled with 
ashlar stones united with mortar at the joints: the surface was paved level with flag- 
stones and bricks. 
12. In the lower station, some upright shores which had been placed in the space 
assigned for the pendulum room were removed, and inclined rafters were substituted. 
The rock was cut level, and the bricks and flagstones were laid immediately on it. 
Brick walls were built enclosing a trapezoidal room nearly representing a square of 
16 feet, with an anteroom, and a third room; and level ceilings were constructed 
above them. 
13. For the galvanic communication between the two stations, two wires covered 
with gutta percha were led underground from the stable to the mouth of the pit ; and 
were then carried down to the bottom of the pit, being supported in the following 
manner. The shaft is divided from top to bottom by a wooden partition or brattice. 
At every 100 feet in the descent, a wooden peg about 6 inches long and 2 inches in 
diameter was fixed in the brattice. The galvanic wires were wrapped round this peg, 
and were pinched fast by a piece of wood which was screwed to the peg. In this 
manner the wires were held perfectly steady, and no part was strained by an ex- 
cessive weight hanging upon them. On reaching the bottom of the shaft, the wires 
were carried horizontally along the top of the galleries, protected by boards of wood, 
till they entered the lower station. The labour of Telegraph Engineers, which was 
