ARC IN AIR BETWEEN OTHER SUBSTANCES 63 



1 E = 26, for 7 = 5 amperes and 1 = 2 mm. 



2 E = 23.86+ .67/7. 



S E = 18.88 + 22.42-3.9;. 



The second of these equations should probably not be 

 considered at all, since other experimenters have shown 

 conclusively that the voltage does not increase with in- 

 creasing current, but the others are sufficient to show that 

 the voltage is not only a function of the current and length 

 of arc, but also of other conditions. Some of the con- 

 ditions under which these formulas were found may be in- 

 dicated by the following. The third formula is only true 

 for a horizontal arc of 2 amperes, the size of the electrodes 

 not being given. The fourth is with rods 16 mm. in 

 diameter with length of arc 2 mm. or less. The fifth is 

 with rods three-eighths inch in diameter with the anode 

 above, while the sixth is for water-cooled electrodes with 

 small currents. 



In addition to these results we have the statement of 

 other experimenters that the curve for the arc between 

 copper terminals does not follow any simple formula. 



1 Lecher, Wien. Sitzungsber., 95, aA, 992; 1887. 



2 Von Lang, Wied. Ann., 31, 391; 1887. 



3 Freedman, Elec. Rev., 37, 253; 1895. 



4 Guy and Zebrikoff, C. R., 145, 169; 1907. 



5 Upson, Phil. Mag., (6), 14, 140; 1908. 



6 Grau and Russ, Phys. ZS., 9, 108; 1908. 



