= 
ELECTRIC LIGHTING AT THE FORTH BRIDGE WORKS. 884 
briefly, as thirteen dynamo machines, developing about one hundred and 
fifty electrical horse-power ; one hundred large arc lamps (of 2,000 can- 
dles each) ; and five hundred incandescent lamps (of 20 candles each), 
A total length of about twelve miles of mains has been laid down in the 
yarious circuits, exclusive of branch wires to lamps. The lighting by 
electricity has been carried on continuously and with satisfactory results 
for nearly two years, by means of the above arrangements. That the 
peculiar requirements of the situation, together with the storms of winter, 
have been successfully coped with, attest the careful and thorough manner 
in which both of the well-known firms who executed the works performed 
the part entrusted to them. 
During that period of working several points of interest have arisen, 
and among them the following :— 
1. The excessively varying conditions which are constantly occurring 
with regard to the outside are lights, both as regards the number in 
actual use, and as to the exact position of each light (dependent greatly 
upon the character of the particular work going on its vicinity, the state 
of the tide, &c.), have been satisfactorily met in the following manner. 
The duty of each series-machine was limited to six arc-lights, as already 
stated, in order to avoid an excessive H. M. F.; the actual number lighted 
being varied between one and six at will, by means of resistance-frames. 
Furthermore, arrangements have been made on a general switch-board 
by which any of the circuits (sometimes as many as six in one locality) 
could be coupled with each other, so that the six lights or less, the 
complement of one machine, might be made to occur, if desired, over a 
circuit of very varied length (sometimes more than a mile long). 
2. The lighting of the large workshops, the drill-roads, &c., demanded 
a combination of arc and of incandescent lights—the relative proportions 
between the two kinds being subject to constant variations. It was also 
necessary that the position should be readily changed, and also that addi- 
tional lights of either kind might be easily obtainable at will. The use of 
* compound-wound ’ dynamos, with the lamps in parallel circuit (the arc 
lamps being in pairs, in series with each other, with a suitable resistance 
in addition), provided for the first condition ; while the second was com- 
plied with by the use of ‘ service-boxes,’ containing ‘ plug-sockets,’ into 
each of which was inserted the plug-end forming the extremity of a 
certain length of flexible twin-leading wire attached to each portable are 
or incandescent lamp. The lanterns in which these several lamps were 
placed varied considerably in form—with arc-lights for outside or for 
workshop use—while for incandescents, hand-lamps, reflecting bulls- 
eyes, divers’ or miners’ lanterns, &c., might be required. 
The advantages attached to this mode of working lamps in parallel 
circuit have proved very considerable. The ease with which lights of 
either kind can be added to or diminished in number, together with the 
comparatively low E. M. F. (110 volts), are points which must be in 
practice appreciated by electrical engineers. At South Queensferry alone 
as many as 50 arc lights (or, in lieu, 600 incandescents) are being 
worked on this principle. Great credit is due to Messrs. Siemens on this 
head, for at the time of their first being used, nothing on so extended 
a scale on the parallel system existed elsewhere ; and certainly the working 
in pair-series was then quite unique. 
3. Perhaps nowhere have more pots of interest arisen than in the 
oo of the working chambers of the deep-water caissons, which 
1885. 3 L 
