414 



HYDROGRAPHICAL SURVEYING [chap. xix. 



their closing, thus keeping all parts of the machine locked. 

 C is the rudder wliich takes up the direction of the current 

 when the levers are unlocked. D is a set of small levers on 

 the rudder in connection with A A. The outer end of the tail 



of the rudder fits into the notches on the outer ring of the 

 frame when the machine is locked, and thus keeps the rudder 

 fixed ; but Avhen the first messenger has started the machine 

 by pressing down B and opening the levers A A, this small 

 lever is raised, and the rudder can revolve freely. 



