AAA^ 



Figure 5 - Wiring Diagram of the Electric Circuit Used with the Double Probe 



pressure changes with a single probe, the sensitivity of the circuit must be pushed to its 

 limit where instability arising from polarization becomes troublesome. Polarization appears 

 to be less troublesome with the double-probe circuit, and potential differences can be obtain- 

 ed to three significant figures with an uncertainty of no more than 1 in the third place. 



The circuit used with the double probe which was developed at Dr. Malavard's labora- 

 tory^ is shown in Figure 5. The potential across the double probe is balanced by the poten- 

 tial across r, which is 





R + T^+r^ 



[13] 



where V is the input potential. The resistances r^ and r^ are the resistances on either arm of 

 a slide wire voltage divider of about 100 ohms, and R is of the order of 100,000 ohms. The 

 exact value of R depends upon the voltage gain or loss in the probe circuit and upon the de- 

 sired range of r^. Then 



