B82 REPORT—1885. 
were constructed to assist in getting in the foundations of the main piers. 
Each of these circular steel caissons, 60 feet in diameter and rather more 
in height, has its sides projecting downwards for about 8 feet below the 
diaphragm or ceiling which extends across the bottom of the cylinder. 
The lower chamber, which is thus formed, is open-mouthed and becomes 
a huge diving-bell. In it a number of workmen, having passed down 
from the surface through a tube 3’ 6” in diameter, excavate the bottom 
(passing the débris up another tube), and thus gradually sink the caisson 
to the requisite depth. This operation is, of course, effected under the 
influence of air compressed according to the height of the water outside. 
In the caissons for the Queensferry main piers, where the bottom was 
of clay, the illumination was effected by means of Swan incandescent 
lamps, twenty in number, of the ordinary 110 volt, 20 c. p. type, used 
throughout the works, but each protected by a strong spherical wire- 
guard for protection from any blow. They were pendent from the ceiling, 
hung on to a hook or wherever else required; each having a certain 
length of twin-wire attached, terminating at the other end in a contact 
plug. The two gutta-percha covered mains, for conveying the electric 
current from the dynamo, pass from the outer air into the air-lock cham- 
ber through a stuffing-box, and thence down the descent-tube into the 
working chamber, where they are led along the ceiling to a ‘ distributing- 
box,’ and then, when required, to a second or even a third ‘box.’ These 
“distributing-boxes’ each consist of two solid copper rods, kept suffi- 
ciently apart and embedded in a wooden block, having a number of square 
openings in it; each opening exposing sufficient of the copper rods to 
allow of a good contact being made. This contact is effected by the 
insertion, when required, of the ‘ plug-end,’ which is at the extremity of 
the flexible lead attached to each lamp; and which, at the moment of in- 
sertion, automatically lights up. 
In the caissons at Inch Garvie a different mode of lighting had to be 
adopted, owing to the rocky bottom, which necessitated blasting ; the 
shock of which would most probably have shattered the incandescent 
lamps. Here three arc-lamps (of the same type as on the surface) have been 
used on two circuits working in parallel (a resistance replacing the fourth 
lamp, which was not required). Above each lamp in the ceiling is a sort 
of hood, into which it is entirely withdrawn during blasting operations, 
in order to avoid any damage. A small pipe in the top of this hood leads 
off the products of combustion into the vertical shaft, and so into the air- 
lock, whence they are discharged into the air. 
The firing of the dynamite charges is performed from the same dynamo 
which does the lighting. A special pair of mains are carried from the 
dynamo down the descent-shaft to a distributing-box on the ceiling of the 
working chamber. The arrangement of the plugs, &c., is the same as for 
the incandescent lamps, a firing fuse of a very simple construction re- 
placing the incandescent lamp. At the top of the descent-shaft the two 
firing mains are both severed, and kept permanently in that state. By 
means of a peculiar double-contact maker, connection can be made 
instantaneously. When everything is ready for firing, the foreman, who 
alone has access to the box where is the contact-maker, fires readily the 
number of charges that may be required. A great deal of the successful 
working of the lighting arrangements in the caissons, as also in other 
ea on the surface, is due to the ingenuity and assiduous attention of 
r. Svdney Baynes, the resident electrician at the Forth Bridge Works. 
