. Radio-activity . ent Volts Current •125 18 •5 7 3 •25 36 1 14 •5 55 2 27 1 67 4 47 2 72 8 64 4 79 16 73 8 85 37-5 81 16 88 112 90 100 94 375 97 335 100 800 100 The results are shown graphically in Fig. 4. From the above tables it is seen that the current at first in-creases nearly in proportion to the voltage. There is no evidenceof complete saturation, although the current increases very slowlyfor large increases of voltage. For example, in Table I. a change ofvoltage from 125 to 25 volts increases the current from 18 to36 °/0 of the maximum, while a change of voltage from 100 to 335volts i
. Radio-activity . ent Volts Current •125 18 •5 7 3 •25 36 1 14 •5 55 2 27 1 67 4 47 2 72 8 64 4 79 16 73 8 85 37-5 81 16 88 112 90 100 94 375 97 335 100 800 100 The results are shown graphically in Fig. 4. From the above tables it is seen that the current at first in-creases nearly in proportion to the voltage. There is no evidenceof complete saturation, although the current increases very slowlyfor large increases of voltage. For example, in Table I. a change ofvoltage from 125 to 25 volts increases the current from 18 to36 °/0 of the maximum, while a change of voltage from 100 to 335volts increases the current only 6 °/0. The variation of the currentper volt (assumed uniform between the range of voltages con-sidered) is thus about 5000 times greater for the former change. n] IONIZATION THEORY OF GASES 33 Taking into consideration the early part of the curves, thecurrent does not reach a practical maximum as soon as would beexpected on the simple ionization theory. It seems probable that 100. 40 60 Volts 100 Fig. 4. the slow increase with the large voltages is due either to an actionof the electric field on the rate of production of ions, or to thedifficulty of removing the ions produced near the surface of theuranium before recombination. It is possible that the presenceof a strong electric field may assist in the separation of ions whichotherwise would not initially escape from the sphere of oneanothers attraction. From the data obtained by Townsend forthe conditions of production of fresh ions at low pressures by themovement of ions through the gas, it seems that the increase ofcurrent cannot be ascribed to an action of the moving ions in thefurther ionization of the gas. 28. The equation expressing the relation between the currentand the voltage is very complicated even in the case of a uniformrate of production of ions between the plates. An approximate e. 3 34 IONIZATION THEORY OF GASES [CH. theory, which is of utility in interpreting the exp
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