64 
POPULAR SCIENCE REVIEW. 
The wall e e T at the side of the Middle Level main is built, say 
three-fifths of the way up, but is left open above that height, 
so as to form a weir. When the storm-waters rise above its 
brim, they fall over into the storm-outlet c and run off at 
x into the Liver Lea. 
The accompanying diagram of the overflow at Regent Circus 
gives a cross section of one of these weirs. 
From Old Ford the brick 
mains proceed under the North 
London Railway until they 
arrive at the Lea, where two 
wrought-iron culverts bridge 
over that river. They are 84 
Pio-. 4. feet in length and 9 feet in 
diameter ; and repose upon 
two solid stone piers — one on each bank. In the two 
tubes there are upwards of 70,000 rivets. We have spoken 
before of the expansion and contraction of ironwork by the 
natural variations of temperature. This is thus in this case 
provided for : — We will, for simplicity's sake, take one culvert 
as an illustration for both. The culvert rides quite free at both 
ends on iron cradles supported on rollers, running on slabs of 
planed iron fixed to the floors of the stone piers. The free 
ends of the culvert project for some distance into the brick 
sewer, and the junction of the expansible culvert with the 
immovable brickwork is made by means of a fold of the best 
milled sheet-lead. In the figure 
c\c 2 , c 3 c 4 represent the won cul- 
vert, the free end of which c 2 c 4 
(having a tendency to expand 
towards e ) projects into the 
open end of the brick main x 1 
x. One edge of the folded 
sheet-lead is fastened by an iron 
plate to the end of the brick 
main all round its mouth. The opposite edge of the lead is 
attached to a flat iron ring passing round the culvert. If the 
culvert expand, the fold is pressed up more acutely, or rather 
out, for the lead-joint constitutes a bulging cylinder all round 
the junction. If the culvert contract, the lead-fold at c is 
drawn out and depressed. The action of this lead-joint, during 
the expansion or contraction of the iron culvert, may be readily 
understood by folding a strip of paper and holding it at each 
end. If we bring our hands together the fold is pushed up ; 
if we draw them apart the fold is lowered and flattened. 
The cradles the culverts rest on are equally carefully con- 
sidered and made. The iron culvert first rests on a broad oval 
Fig. 5. Junction of iron culvert across 
the Lea, with the brick sewer. 
MAIN 
D RAI N 
