266 THE DIVING BELL. 



Subtracting the second from the first, we have 

 wk (DC - EC) = wk x DE, 



for the resultant i'oree which urges the water at C from left 

 to right, and hence there will be a continuous flow of water 

 from the upper to the lower vessel. 



It will be observed that the direction of the flow is wholly 

 due to the fact that the level of the water in B is below that 

 of the water in A. It is not necessary therefore that the 

 longer branch should be immersed in the water; so long 

 as the end B of the tube is below the water surface in A, 

 the water will continue to flow through the tube ACB, 

 until either the surface in A has fallen below the end of the 

 tube, or, if the siphon be long enough, until the surface in 

 A has descended so far that its depth below C is greater 

 than h. 



SCH. The siphon is often used to drain ponds, marshes, 

 and canals, and when used for this purpose it is made of 

 leather, or stout canvas, like the common hose. 



142. The Diving Bell. This is a large bell-shaped 

 vessel made of iron, open at the bottom, and containing 

 seats for several persons. Its weight is greater than that of 

 the water it would contain, and when lowered by a chain 

 into the water, the air which it contains becomes more and 

 more compressed as it sinks, in consequence of the increas- 

 ing pressure to which it is subject. As the volume of air 

 diminishes the water rises in the bell ; but the air will 

 prevent the water from rising high in the bell, and the 

 persons seated within are thus enabled to descend to con- 

 siderable depths and to carry on their operations in safety. 

 When the surface of the water 'within the bell is at a depth 

 of 33 feet below the outer surface the bell will be half filled 

 with water. The bell is supplied with fresh air from above 

 by a flexible tube connected with an air pump, and may be 



