years and that its valves had functioned at least 2500 million times 

 without ever breaking down. Indeed, the human heart has no metal in 

 any part of its construction ; it is entirely made of flexible membranes : 

 why not take them for a model ? 



The membranes are in synthetic rubber impervious to the action of 

 petrol, and the seatings are of stainless steel. Thus there is no fear of 

 the membranes and seatings adhering. 



To make it even safer, I placed on the upper part of the tower a 

 U-shaped iron tube containing mercury, connected with the central 

 compartment of the float (see page 77 and Fig. 8). The fact that it lost 

 no mercury proves that our valve has never been blocked. 



Appendix 11 



The Control Valve 



In the top of the vessel containing the stabilizing petrol is an 

 opening of 3-1 sq. in. section, closed by the valve flap, in the centre 

 of which is fixed a vertical iron rod ; this latter penetrates into a coil : 

 if an electric current is passed through the coil the rod is attracted and 

 the valve opens. When the current is cut ofl", it falls back and closes 

 the opening. To decrease the number of ampere-turns necessary for 

 the operation of this valve the magnetic circuit is closed by soft iron, 

 except in the part which is situated between the rod described, and an 

 iron core placed in the upper part of the coil. To lift the valve a rather 

 strong current is necessary, but when the rod has reached the imme- 

 diate neighbourhood of the core, the magnetic flux circulating almost 

 entirely in iron requires for its maintenance only a small current. One 

 takes advantage of this by arranging the switch so that a heavy current 

 is maintained for only two seconds. This detail has its importance 

 because the reserve of energy that our battery can furnish is limited and, 

 above all, because a heavy current would at length generate too much 

 heat in the coil and in the plugs of the passages through the cabin wall. 



The pressure that the petrol exercises upon the base of the valve 

 flap is variable. When the vessel containing the petrol is still full, it 

 produces upon the 3-1 sq. in. of the section a force of 4-4 lb., but this 

 force moves towards zero progressively as the petrol in the reservoir is 

 replaced by water. To compensate this variation in force, the valve is 

 loaded by a rod whose cross-sectional area is equal to that of the valve 



[ 179 ] 



