197 
dieiifcs, and this is in accordance with the prersent liypothesis. 
For, wlien the currents are so large, the value of nn^ is 
great, and the effects of general recombination must be con- 
siderable, unless tlie potential gradient is inuch increased. In 
fact, the general characteristic of these curves is tliat the larger 
the current the higher the potential gradient niust be at the 
point where the effects of altering the depth of the chamber 
cease to be visible. 
Several observers have determined the form of the curve 
connecting current and potential gradient, and have calcu- 
lated therefrom the recombination co-efHcient- Let us now 
consider the result of neglecting the effects of initial recom- 
bination in these calculations. 
If the currents are very great, the effects of initial re- 
combination may be small as compared to those of general 
recombination. But they must always be there, and iheir 
effect will be of greater relative importance when the current 
is made smaller, either by using a weaker source of ionisa- 
tion or by lessening the width of the ionisatioii chamber. If 
both effects are ascribed to one cause, whose influence is 
measured by a, then a must be given a value which is ficti- 
tiously large. The smaller the chamber, the greater the appa- 
rent value of a must be ; and this is actually the case, as 
found and remarked upon by Retschinsky. For when the 
chamber is very small the effects of general recombination 
ought to be small : and if, as is the case, there is still a con- 
siderable lack of saturation at moderate voltag'es, the whole 
of which is ascribed to general recombination, the value found 
for <'- must be very great- It is jDOssible to find any desired 
value of <'■ in this way, if only the currents are made small 
enough. This is especially true if we use the first formula 
employed by Retschinsky, and ascribed by him to Riecke. In 
this the determination of a depends on the difference between 
two current-values taken from the upper j^art of the curve 
where the slope is due rather to initial than to general recom- 
bination- To make this point clear consider the following 
determinations of a : — 
Retschinsky gives the following form of Riecke's equa- 
tion where the quantities are expressed in electrostatic 
units : — 
c- i c I 
where C' = saturation current pei' s(|. cm. of electrode 
c*-^ current for a pottMitial gradient l'\ 
1 = (lt^})tli of chamber. 
