Page 262 - Third Book of Reading Lessons

READING LESSONS. 261
at the upper ori ce of a cock expressly tted r that purp9se. When this is done, the divers turn the handle which stops the cock; so that if any more air were to get into the cavity, it could no longer be dis­ charged through the ori ce as be re. If, there re, the divers wish to raise themselves, they turn the cock, by which a communication is made between the upper and under cavities of the bell. The con­ sequence is, that a quantity of air immediately enters the upper cavity, and rces out a quantity of the water contained in it, and thus renders the bell light­ er by the whole weight of the water which is dis­ placed: thus, if a certain quantity of air is admitted into the upper cavity, the bell will descend very slow­ ly; if a greater quantity, it will neither ascend nor descend, but remain stationary; and if a large ·quan­ tity of air be still admitted, it will rise to the top. It should be observed, however, that the air which is thus let out into the upper cavity, must immediately be replaced om the air-barrel; and the air is to be let out very slowly, or the bell will rise to the top with so great a velocity, that the divers will be in danger of being shaken out of their seats. But by llowing these directions, every possible accidnt may be prevented, and persons may descend to a very great depth, without the smallest apprehension of danger. The bell also becomes so easily managed in the water, that it may be conducted from one place to another by a small boat, with the greatest ease,
and with perfect sa ty to those within.
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