422 



TABLE 431.— POTENTIAL NECESSARY TO PRODUCE A SPARK IN 

 BETWEEN MORE WIDELY SEPARATED ELECTRODES 



AIR 



The specially constructed electrodes for the 

 columns headed "cup electrodes" had the 

 form of a projecting knob 3 cm in diameter 

 and having a height of 4.5 mm and 1.5 mm 

 respectively, attached to the plane face of the 

 electrodes. These electrodes give a very sat- 

 isfactory linear relation between the spark 

 lengths and the voltage throughout the range 

 studied. 



TABLE 432.— EFFECT OF THE PRESSURE OF THE AIR ON THE DIELECTRIC 



STRENGTH 



Voltages are given for different, spark lengths /. 



TABLE 433.— POTENTIALS IN VOLTS TO PRODUCE A SPARK IN KEROSENE 



SMITHSONIAN PHYSICAL TABLES 



