152 Prof. E. Rutherford on Uranium Radiation and 



The general relation between the current through the gas and 

 the E.M.F. acting on it is very similar to that obtained for 

 gases exposed to Rontgen radiation. The current at first 

 increases nearly proportionally with the E.M.F. (provided 

 the E.M.F/s of contact between the metals are taken into 

 account), then more slowly, till finally a stage is reached, 

 which may be termed the " saturation stage," where there is 

 only a very slight increase of current with a very large 

 increase of electromotive force. As far as experiments have 

 gone, uranium oxide, when immersed in gases which do not 

 attack it, gives out a constant radiation at a definite tempera- 

 ture, and the variation of the intensity of radiation with the 

 temperature over the ordinary atmospheric range is inap- 

 preciable. For this reason it is possible to do more accurate 

 work with uranium radiation than with Rontgen radiation, 

 for it is almost impossible to get a really steady source of 

 a?-rays for any length of time. 



It was the object of these experiments to determine the 

 relation between current and electromotive force with accuracy, 

 and to see whether the gas really becomes saturated ; i. €., 

 whether the current appreciably increases with electromotive 

 forces when the electromotive forces are great, but still not 

 sufficient to break down the gas and to produce conduction 

 in the gas without the uranium radiation. 



A null method was devised to measure the current, in order 

 to be independent of the electrometer as a measuring instru- 

 ment and to merely use it as an indicator of difference of 

 potential. 



Rff. 12. 



Ear 



E/lffTH 



Fig. 12 shows the general arrangement of the experiment. 

 A and B were two insulated parallel zinc plates : on the lower 



