8o 



THE ELECTRIC ARC 



between voltage and length of the arc for different pres- 

 sures. The voltage is here shown to be a linear function 

 of the length of the arc for all pressures. This is expressed 

 by the formula E = a + bl, where a and b are quantities 

 depending on the pressure of the gas. a would be approx- 



55 



30 



< 25 



20 



15 



10 



3.5-* 



2.5 



1.5 



0.5 



50 100 150 200 250 300 350 400 450 500 550 600 650 700 750 



PRESSURE IN MM. 

 FIG. 25. 



imately the same as the sum of the anode and cathode 

 drops, and b the same as the electric force through the arc. 

 Their values for different pressure are plotted in Fig. 25. 

 The values for a vary in the same way as those for the 

 cathode and anode drop, as shown in Fig. 22, and the 

 values for b in the same way as the values for the electric 

 force as found by myself. 1 



1 Phys. Rev., 19, 122; 1904. 



