Besides the pear-shaped Swan lamp, in
which the glowing or incandescence is carried on _in vacuo_, there is an
outer lantern, the invention of Mr. David Graham, consisting of a strong
glass globe, air-tight, protected with steel guards. Each lamp was also
connected with two different forms of Graham's patent safety air tight
contacts and switches for cutting off and letting on the current, the
effect of which, it is believed, would be to render the lamps quite
safe, even in the presence of explosive gas. At first the intention
was to employ the fan-engine to drive the dynamo-electric machine or
generator, but this was departed from, and an engine of 12 horse-power
was erected in the workshops on the surface for the purpose. From the
generator the electric cables, two in number, are conducted along the
roof of the workshops over ordinary telegraph poles to the pit-head at
No. 2 shaft, and thence down into the workings. From the ridge of the
workshops to the pithead, a distance of several hundred yards, the
cables consist of ordinary copper wire, three-eighths of an inch in
diameter; inside the workshop and below ground, to allow of their safe
handling, they are composed of insulated wires, while on the way down
the shaft they are inclosed in a galvanized tube.
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