payerne's hydrostat. 



655 



lower compartments is a third, communicating with the others 

 only by stop-cocks. The upper compartment is called the be- 

 tween decks, and the middle one the orlop deck. All round 

 the hold and the orlop deck runs an air-tight gallery connected 

 with the other compartments only by stop-cocks. The lower 

 part of this gallery contains the ballast, while its upper part 

 is fill with air or water, according as it is desired to float or 

 sink. 



payerne's submarine hydrostat. 



When the hydrostat lloats, the hold and a portion of the 

 shaft are filled with water; while the orlop deck, its galierj 

 and the between decks are full of air. The workmen are in 

 the between decks, where are lifting and forcing pumps. When 

 it is desired to sink the hydrostat, the door of the shaft and 

 the hatch of the between decks are closed water and air-tight 

 The pump is then worked so as to draw water from the out- 

 side and fill the urlop deck and its gallery. At the same time 

 the force-pump is used to force air into the hold through a 

 pipe no^necting the hold and the orlop deck, and furnished 



