THE ULTRASTABLE SYSTEM 



8/8 



way. In front of each magnet is a trough of water ; electrodes 

 at each end provide a potential gradient. The magnet carries 

 a wire which dips into the water, picks up a potential depending 

 on the position of the magnet, and sends it to the grid of the 

 triode. J provides the anode-potential at 150 V., while // is at 

 180 V. ; so £ carries a constant current. If the grid-potential 

 allows just this current to pass through the valve, then no current 

 will flow through the output. But if the valve passes more, or 

 less, current than this, the output circuit will carry the difference 



s©tS 



ZP 



K<*& 



^ 



u _^ 



^ 



&^s, 



Figure 8/8/3 : Wiring diagram of one unit. (The letters are explained 



in the text.) 



in one direction or the other. So after E is adjusted, the output 

 is approximately proportional to il/'s deviation from its central 

 position. 



Next, the units are joined together so that each sends its 

 output to the other three ; and thereby each receives an input 

 from each of the other three. 



These inputs act on the unit's magnet through the coils A, 



B, and C, so that the torque on the magnet is approximately 

 proportional to the algebraic sum of the currents in A, B, and 



C. (D also affects M as a self -feedback.) But before each 

 input current reaches its coil, it passes through a commutator 



95 



