CONTEMPORARY ADVANCES IN PHYSICS 



95 



leading up to breakdown, as steady voltage; these data therefore 

 indicate that up at least to frequencies of the order of a hundred 

 thousand, an oscillating voltage causes breakdown when its amplitude 

 becomes the same as the steady voltage which can have the like 

 effect; and this is in agreement with other observations. 



The curves which depart from the straight line correspond to 



0.1 0.2 0.3 0.4 0.5 06 



CENTIMETERS 



Fig. 12 — Curves of sparking-potential versus distance, in atmospheric air, be- 

 tween spherical electrodes of 2.5-cm. diameter, at various frequencies. (Lassen, 

 Arch. f. Elektrotech.) 



various higher frequencies, indicated on the figure. The "critical 

 distance" at which the departure occurs is inversely proportional to the 

 2/3 power of the frequency. If the data are plotted differently, spark- 

 ing-potential versus frequency for the various gap-widths, each curve is 

 parallel to the axis of abscissae up to a "critical frequency" which 

 increases with decrease of distance (Fig. 13). Beyond the critical 

 frequency, each curve drops off, the ordinate sinking by fifteen to 



