10 TECHNOLOGY. 
The tunnel is situated between Wapping and Rotherhithe (see the plan, 
Jig. 28) at the only point between London Bridge and Greenwich where it. 
could be driven without endangering the foundations of the bridges across the 
Thames. The banks of the river at this place are but 1200 feet distant from 
each other. Formerly it was necessary to make a circuit of four miles to 
pass from one side of the river to the other. 
The joint-stock company which constructed the tunnel was formed in 
1824, and the work was commenced in the following year by the construc- 
tion of a cylinder of brick, fifty feet in diameter, three feet thick, and forty- 
two feet high, on the Rotherhithe shore, 150 feet from the river. This 
cylinder rested on a cast iron ring, sharp on its lower edge, and its masonry 
was well connected by iron rings and anchors. On its top was erected a 
steam-engine of thirty horse-power for the purpose of elevating the earth 
and water from the excavation; the earth being dug away from under the 
cylinder, it gradually descended until in this manner a walled shaft of 
sixty-five feet depth was obtained; a second shaft eighty feet deep was sunk 
in the first one, to serve as a reservoir for the water. The tunnel com- 
mences at a depth of sixty-three feet; it was excavated thirty-eight feet 
wide and twenty-two and a half feet high, as it was to afford room for two 
arches, each fifteen feet high, and having a footway besides the carriage- 
way (pl. 1, jig. 80). The entrance to the tunnel from the shaft is shown in 
jig. 84. The excavation of the tunnel was commenced on the first of 
January, 1826. For every foot in length about 45-50 tons of earth were 
removed and delivered at the head of the shaft by the steam-engine, and 
5,500 bricks were required for the masonry. Although the tunnel descends 
about three feet in every hundred, yet it approaches the bed of the river 
near the middle to within ten feet (jig. 29). Still no aceident happened 
until the 18th of May, 1827, when at a distance of 544 feet from the shaft 
the water broke in with such violence that within fifteen minutes the tunnel 
was filled with water and about 1,000 tons of sand. On examining the 
break with the diving-bell it was found that the arches had not been 
damaged, and that the shield remained in its place. The break was filled 
with 3,000 earth bags, each containing a ton of clay, and the water being 
pumped out, the work was re-ccommenced in September, but progressed very 
slowly, as the workmen were much inconvenienced by fire-damp, and the 
work was often dangerous. Fifty-two feet more were completed when, on 
the 12th of January, 1828, the water broke in a second time and filled the 
tunnel in ten minutes. On this occasion six workmen lost their lives. 
This break having also been closed by means of 4,000 tons of clay in bags, 
the water was again pumped out; but the work stopped here for want of 
funds. Seven years afterwards, when government agreed to advance 
all the funds required, the work was taken up again, but progressed very 
slowly on account of the difficulties of the ground. Three more breaks 
also occurred, but one life only was lost. In January, 1841, the tunnel had 
reached the opposite bank, a distance of 1,140 feet, and on the 13th of 
August of the same year Sir i. Brunel walked for the first time below the 
Thames from one shore to the other. On the 25th of March, 1843, the 
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