[CARR] AN EXTENSION OF PASCHEN’S LAW 169 
The distance between the electrodes was then varied and five 
different sets of readings were taken in air with the electrodes 1, 2, 
3, 5, and 10 mm. apart, respectively. The complete set of numbers 
for these different spark lengths is given in Table I., and curves 
showing the readings taken over that portion of the range of pressure 
below 5 mm. of mercury are exhibited in Fig. IT. 
It is apparent from the relative positions of these curves in the 
figure, that at points at and below the critical pressures, with a given 
potential difference applied to the electrodes, the pressures at which 
discharges occurred regularly decreased as the distance between the 
electrodes was increased. But a critical examination of the curves 
and also a reference to the numbers which they represent show that 
Paschen’s law is rigidly applicable over the whole series of discharge 
potentials recorded. 
For example, the pressures at which discharge took place with 
an applied potential of 1800 volts were, for the different distances 
between the electrodes, approximately :— 




Distance between electrodes Discharge pressures in 
in mm. mm. of mercury. 
1 1°05 
2 536 
3 351 
5 216 
10 ‘105 


and it will be seen that the numbers in column ? are almost exactly 
in inverse proportion to the numbers in column 1. 
Again, with an applied potential of 500 volts (say), the approxim- 
ate pressures at which discharge occurred were :— 




Distance between the electrodes Discharge potential in 
in mm. mm. of mercury. 
i 2°35 
2 1°30 
3 ‘804 
5 ‘517 
10 *259 

seca lite, 002 
