Descents in a Diving Bell. 329 
used on a ship’s deck, on the top. He was half an hour under water 
more than twenty feet deep, and had light enough to read and write. | 
A constant supply of fresh air was given by means of a forcing pump, 
and the respiration was not in the least affected. A diving bell of the 
above dimensions may hold four persons. I mention these facts for the 
benefit of those who may have mason work to do under water. 
The writer of the article “ diving bell” in the Edinburgh Encyclope- 
dia of Dr. Brewster, republished in Philadelphia, by Joseph Parker, 
says, “ the diving bell appears at first sight to be capable of very ex- 
tensive use to engineers, in constructing the foundation of bridges, 
piers, sluices, and other works of hydraulic arcbitecture. It would 
obviate the necessity of coffer-dams to inclose the area of the foun- 
dation, and of the engines for drawing out the water, preparations 
which are generally the occasion of greater labor and expense than 
the masonry or other work to be performed ; and surveyors might 
have the means of examining the state of their work under water, or 
of making trifling repairs, which from the great difficulty at present 
of gaining access to the parts, are neglected and deferred, until they 
become of serious extent.” He refers to the diving bell having been 
used on two important occasions by the eminent Smeaton: one was 
to repair some of the piers of the bridge over the Tyne, at Hexham, 
in Northumberland ; and by it, he was enabled to fill the cavities be- 
neath them with large rough stones. Another was for the purpose of 
getting up a quantity of large stones which some years before 
had been thrown into the sea at Ramsgate harbor, many of which 
were a ton in weight: one hundred tons were got up in the course of 
two months. Had a diving bell been used to examine the cause of 
the immense leakage of the western coffer-dam, when the first perma- 
ment bridge on the Schuylkill, at the west end of High-street, was in 
_ progress of erection in the year 1801, much time, labor and expense 
would have been saved. ‘The cause of this is worth inserting. 
When the British were in possession of Philadelphia in 1777, 
they constructed a bridge composed of pontoons, over the river, and 
two of the piles of the coffer-dam were obstructed by a part of one of 
those boats which had been accidentally sunk, twenty-eight feet be- 
low common low water. It occupied part of the area of the dam, 
with one end projecting under two of the piles of the inner row, and 
had nearly rendered the erection abortive, admitting the water which 
could not, for a long time, be overcome by all the pumps employed, 
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