34 



Mil. O. W i;K HARDSON ON THE IONISATION 



the square root. The above numbers yield, for the maximum current the above wire 

 was capable of furnishing, at 730 C. the value I2xl0~ 12 ampere, or, per square 

 centimetre of surface, 54 x 10~ 13 ampere. 



The following series refer to a somewhat higher temperature (820 C.) and furnish 

 a more complete test of the way the formula works at higher pressures. In this case 

 a was taken = 5G x I0~ ia ampere and ft = 4'0 (millims. of mercury)*. 



The maximum value of the positive ionisation in oxygen at 820 C. appears from 

 these numbers to be =2'5 x 10~ 10 ampere per square centimetre. The values of the above 

 leaks at the lowest pressures are probably somewhat high, as it was found to be 

 impracticable to wait long enough to be certain that equilibrium had become fully 

 established. 



We have seen that the assumption that the denominator in the expression for the 

 positive ionisation is of the form /8 + P* is an approximation which will only hold at 



