STEAM NAVIGATION. 



fig. 8 is represented a transverse section of a part of a steam- 

 vessel ; w is the water-line of the boiler, B is the mouth of a 

 blow-off pipe, placed near the bottom of the boiler. This pipe 

 rises to A, and turning in the horizontal direction, A c, is con- 

 ducted to a tank T, which contains exactly a ton of water. This 

 pipe communicates with the tank by a cock D, governed by a 

 lever H. When this lever is moved to D', the cock D is open, and 

 when it is moved to K, the cock D is closed. From the same tank 

 there proceeds another*pipe E, which issues from the side of the 

 vessel into the sea, governed by a cock F, which is likewise put in 



Fig. 8. 



connection with the lever IT, so that it shall be opened when the 

 lever H is drawn to the position F', the cock D' being closed in all 

 positions of the lever between K and F'. Thus, whenever the 

 cock F communicating with the sea is open, the cock D communi- 

 cating with the boiler is closed, and vice versa, both cocks being 

 closed when the lever is in the intermediate position K. By this- 

 arrangement the boiler cannot, by any neglect in blowing off, be 

 left in communication with the sea, nor can more than a ton 

 of water be discharged except by the immediate act of the 

 140 



