the area that the copper may occupy. It results in a greater consump- 

 tion of electrical energy than would have been needed with simple 

 cotton insulation. 



This valve requires, it is easy to see, a greater number of ampere- 

 turns to stop the flowing out of the ballast once it has started than 

 to hold it in position. In order to economize the energy of our 

 accumulators, we can carry on with a retaining current which is only 

 half the current employed to stop the outflow. With this in view, the 



Fig. 17. Magnetic valve controlling the release of the iron pellets 



a. Tub c. Non-magnetic substance 



b. Electro-magnet f/. Coils 



coils of the two valves are normally connected in series and only in 

 parallel during a few seconds at the moment when the pilot wants to 

 stop the outflow of ballast. 



We give here some numerical data concerning the unballasting of the 

 Trieste. Two ballast tubs, each of which weighs a ton when empty. 

 Contents of each tub : 4-5 tons of iron pellets. Diameter of the outlet 



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