shaft can be jammed and even may break. Moreover, the external 

 pressure of the water jeopardizes the free play of the system. We must 

 then give up the stuffing-box and any direct mechanical drive. 



In these conditions I see no other solution than to use an electric 

 control, but the very word electricity calls up the double spectre of 

 short-circuit and bad connection. Let us put the problem the other 

 way: the electric current will retain the ballast and when the current 

 is switched off, whether intentionally or accidentally, the ballast will 

 fall. It is the electro-magnet which fulfils these conditions: as long 

 as the current runs through its coil, it will retain the burden: it will 

 drop it as soon as the current is cut off. 



The electro-magnet in its conventional form has, however, a dis- 

 advantage. Each magnet can hold and release only one mass, and that 

 would only permit of unballasting in large portions, while it is essential 

 that the pilot should be able, in some circumstances, to unballast in 

 small amounts. I had used small shot when I was making my ascents 

 into the stratosphere and now I used it here and stored it in two big 

 tanks built into the float. Here is the arrangement we adopted and 

 which proved to be to our entire satisfaction. The lower part of the 

 storage tank is funnel-shaped : the orifice is encircled with an electric 

 coil. If the electric current is running through it, the small shot is 

 magnetized : it then forms a compact mass which plugs the orifice. If 

 the current is cut, the shot flows like sand from a sand-box. If the cur- 

 rent is switched on, the flow ceases instantly (see Figs. 9, i6 and 17).! 



Besides the iron shot, the first bathyscaphe, the FNRS 2, carried 

 three other sorts of ballast : tubs filled with scrap iron, held in place 

 by electro-magnets and capable of being unballasted one by one; 

 gravel stored in four big tanks closed at the bottom by flap-valves, 

 also held shut by electro-magnets. If one switched off the current 

 from one of these magnets, the valve opened and the contents of the 

 tank flowed out at once. Last, in their turn, each of the two heavy 

 storage batteries was suspended beneath the float to the armature 

 of an electro-magnet : thus the batteries served as emergency ballast 

 and could be sacrificed in case of necessity. ^ 



1 This is the device with which the Trieste is equipped. We shall see later that 

 the storage tanks can be unballasted as well if necessary, for example, if the orifice 

 becomes obstructed by a foreign body. 



2 This last mode of unballasting has also been adopted for the French bathy- 

 scaphe FNRS 3. 



[33] 



