and whose density is equal to that of water. This rod consists of an 

 aluminium tube filled with petrol. Its length is equal to the height of 

 the vessel containing stabilizing petrol, i.e. 11-55 feet. Thus its 

 apparent weight will always exactly compensate the variable thrust of 

 the petrol upon the valve. This design, at first sight, seems perfect. 

 It has, however, a defect ; when the valve opens, the petrol flows out 

 and necessarily the pressure of the liquid decreases at this moment. 

 (The kinetic energy is acquired at the expense of the potential energy, 



which is represented by the 

 pressure, according to a funda- 

 mental law of hydrodynamics.) 

 It follows that the force that 

 must be exerted to lift the 

 valve must be increased pro- 

 gressively as this rises. The 

 compensation is thus no longer 

 perfect. 



Technical problems often 



appear thus: you search up 



to the moment when you find 



one solution, then you go on 



to other problems; and it is 



only later that you see you 



have indeed fouAd a solution, 



but not the solution, the only 



one, generally, which was perfect. That is what happened with my 



valve. I was satisfied to see it functioning, although the valve flap could 



not be raised as much as we should have liked. 



It was only a little while before our leaving for Ponza that I found 

 the solution : its simplicity is such that I should have found it at the 

 first attempt. It is derived directly from the compensated valve of a 

 steam engine that Professor Stodola explained to us when I was a 

 student at Zurich. I am sure that I should have thought of it earlier, 

 if I had not been fascinated by the invention of my compensating rod. 

 The principle of this compensated control valve will be understood at 

 once by a glance at Figs. 26 and 27. The first is diagrammatic. Coming 

 from the reservoir tz, the petrol enters the distributing chamber. This 

 has two openings, one at the top, the other at the bottom. Each of these 

 openings is closed on the upper side by a flap : the two flaps b and c 



[ 180] 



Fig. 26. Diagram of the electrically-com- 

 pensated control valve 



