4f, 



MI:, o. AV. mriiAunsox ON THE TOMSATION 



200 



150 



5 100 



10 20 30 



VOIDS 

 Fig. 14. 



4O 



only appears to attain to the high value of the leak in hydrogen with extreme 

 slowness when heated in that gas. It semis very difficult to reconcile these state- 

 ments if the only time effect occurring is the diffusion of hydrogen into and out of 

 the wire. 



The relation between the negative leak in hydrogen and the applied electromotive 



force was next examined. It was found that the normal 

 curve, exhibiting saturation and a definite relation between 

 current and electromotive force, could only be obtained 

 under very restricted conditions. The normal relation 

 referred to is that exhibited by fig. 14. This experiment 

 was made with the wire 0'2 millim. in diameter and 

 0'66 sq. centim. effective area; the pressure of hydrogen 

 was 3 '8 millims. and the temperature 900 0. 



The heating current caused a fall of potential of about 

 5 volts along the filament ; the potentials given are the potentials of the middle point 

 of the filament. The unit of current is l'67x!0~ 10 ampere. The increase in the 

 current with voltages greater than 20 indicates that ionisation by collisions was 

 beginning to come in. 



On pushing these experiments to higher potentials, it was found that the current 

 ceased to be a definite function of the applied E.M.F. and varied in a curious way 

 with the time. The mystery was cleared up when considerably higher potentials 

 were applied. The experiments were carried out at 1084 C. with a wire O'l millim. 

 in diameter and an effective area of 0'214 sq. centim. The pressure was 1'77 millims. ; 

 the unit of current to which the following numbers refer is 10~ 8 ampere. It was 

 found that under a high voltage the steady current was smaller than under a low 

 one. For instance, under 19 volts the wire had been giving a steady negative leak 

 of about 147 divisions. At a certain instant the voltage was changed to 286, when 

 the following values of the current were obtained after the intervals of time 

 stated : 



The voltage was now reduced to 80, when the current was found to remain almost 

 steady for some time at 7 divisions. It did not, however, stay at this value, but 

 after a time began to increase, slowly at first, then more rapidly, then more slowly 

 again, until it finally became steady at about 220 divisions. This great reduction of 

 the leak by applying a big voltage and subsequent slow increase under a low voltage 



