iC THE BOTTOM OF THE SEA. 



reversed. In the fixed bottom there is a small hole, 

 furnished with a valve, which opens from the exterior 

 to the interior, so that the water passes through and 

 fills the space between the descending piston and the 

 fixed bottom. This being done, the valve is closed 

 by the action of a spring, and the water contained in 

 the pail is isolated. 



If this water contained any quantity of compressed 

 air, nothing would be able to resist its expansive 

 power when it was drawn to the surface, and the 

 pressure of the exterior w'ater ceased to act. It 

 would then burst the apparatus and escape. As a 

 safeguard against this violence, a free issue is 

 prepared, sufficient to serve for any possible expan- 

 sion of the air in the water. In the fixed bottom 

 there is a passage communicating with a bladder, 

 which is empty and folded up when the apparatus is 

 let down into the sea, but which receives whatever 

 gas or air the water in the pail may disengage as it 

 ascends, and thus returns to the surface more or less 

 inflated. The operator then closes the stopcocks 

 with which the passage of communication between 

 the pail and the bladder is fitted ; and having sepa- 

 rated the latter, he proceeds to measure and analyse 

 the air contained in it. Having done this, he can 

 study at his leisure the water enclosed in the pail, 

 and whatever matter it holds in solution. 



