Radio-active Products of Short Life. 637 



The straight line marked " Diffused Radiation " gives the 

 effect observed when tie reflector is uncharged. The upper 



Fiar. 3. 



10 £0 30 



77/W£ IN M//VUTES 



curve was obtained when the reflector was charged by a 

 Wimshurst machine to a potential of about 10,000 volts, the 

 distance between source aud reflector being 5 cm. After 

 18 minutes the reflector was again earthed. By subtracting 

 the diffused radiation from the latter part of the upper curve, 

 the straight line marked "Act D " was obtained. It wilJ be 

 noticed that the two branches of the upper curve meet ; a 

 proof that no product of period of a few seconds has been 

 deposited by recoil. 



Sensibility of the new method. 



A brief discussion will now be given of the possibilities 

 of the new method for detection of products of very short 

 life. The time interval between the formation of a new 

 product and the detection of its effect depends on two factors: 

 (1) the interval required for deposition of the active matter 

 on the rotating disk, (2) the interval between deposition and 

 measurement — which is determined by the angular distance 

 of the detecting vessel from the source and the speed of 

 rotation of the disk. The minimum time lost by a charged 



