480 Prof. C. Barus on the Ionization 



needed in the reductions. The potential in these experiments 

 usually begins with about 40 volts. The table also contains 

 the value of E/E' for observations half a minute apart, two 

 of these being available for each colour as specified. The 

 current was computed as follows : — For a very short time 

 after charging the fall of potential is appreciably logarithmic. 

 Hence E/E / = 10"~ z(<- *' ) may be assumed, where E and W are 

 the potential-differences at the times t and t' in minutes, and 

 x a constant for a given colour in the tube. Hence 



-C(dE/dt) = CEx Aogl0 = 60i, 



if C is the aggregate capacity of the electrometer and the 

 condenser, and i the current flowing radially through it. 

 Since 



log (E/E'= - a (t-t'), or -#=81ogE/&, 



the table furnishes these data with E, to compute i relatively; 

 and it was thought superfluous to supply the factor Clog ] 0/60, 

 sharply. Its estimated electrostatic value is about 230/60, as 

 the combined capacity of the electrometer (60 cm.) and the 

 condenser (39 cm.) is about 99 cm., roughly. This would 

 make the capacity 1*1/10 10 farads, and the factor is 4'2/10 12 . 

 The table shows a few values of i in coulombs ; but the quantity 

 «£, being more immediately derived from the observations, will 

 be chiefly discussed below, and has therefore been constructed 

 in terms of V, the air-volume per minute, in fig. 3. The 

 colours seen in the steam-tube are added to each point, as 

 explained in the table. 



5. The effect of the presence or absence of this electrical 

 current on the colour-tube is quite inappreciable, no change 

 of tint or suggestion of change occurring on charging the 

 condenser. J gave the question an additionally severe test 

 (up to 300 volts), showing that only an insignificant part of 

 the nuclei present take part in the convection of electricity 

 radially across the condenser, as detailed in an earlier paper. 



6. On the other hand, however, the current varies with the 

 number of nuclei present, no matter how small the relative 

 quantity actually promoting electric conduction. This is 

 fairly well shown in the chart (fig. 3) already described, 

 which graphically reproduces Table J. Finally, in fig. 4 the 

 radial electrical currents are given as ordinates, the corre- 

 sponding volumes per minute (V) of the air passing longitu- 

 tudinally through the condenser as abscissas. The relation 

 of saturated litres per minute longitudinally and coulombs 

 per second radially is thus apparent for the second and fourth 

 series. The other series, if supplied, would add nothing new. 



