876 Drs. Russ and Makower : Deflexion by Electrostatic 



i recoils and, if so, its sign ; the magnitude of the deflexion 

 of the recoiling atoms by an electric field has also been 

 determined. A great number of experiments has been made 

 by different methods, which show that the " recoil-atoms " * 

 of radium B are positively charged. The process of the form- 

 ation of radium B from radium A would therefore seem to be 

 accompanied by the expulsion of /3 rays as well as a. rays, 

 though the speed of the former may be too small to allow of 

 their detection by ordinary methods. 



Preliminary Experiments. 



In the earlier experiments, two insulated brass plates 

 3*5 centimetres long and J 1 centimetres wide were mounted 

 at a distance of one millimetre apart inside a 

 glass vessel which could be rapidly exhausted to 

 a high vacuum. A platinum wire was exposed to 

 radium emanation for about ten minutes to obtain 

 as much radium A on it as possible and then trans- 

 ferred to a tube which could be quickly exhausted, 

 contained in a furnace at about 400° C. It was 

 found that the emanation adhering to the wire could 

 in this way be completely removed. The wire 

 was then mounted at W, as shown in fig. 1, so ^ B 

 that the " recoil-stream " from it was projected 

 symmetrically between the two plates A and B. 

 An electric field could be applied by connecting 

 the two plates respectively to the two terminals 

 of a storage battery by leads sealed through the VJ 



glass vessel. 



After ten minutes' exposure in vacuo the plates were 

 removed from the vessel and the distribution of activity on 

 each tested by mounting them in turn on a movable plat- 

 form, and bringing successive strips of the plates under a 

 rectangular window 3 centimetres long and 3 millimetres 

 wide, cut in the base of an electroscope and closed by an 

 aluminium leaf. The a and /3 radiation from the section 

 of the plate just under the window could thus enter the 

 electroscope, but the radiation from the rest of the plates 

 was prevented by lead screens from contributing to the 

 ionization inside the electroscope. From such measurements 

 the number of " recoil-atoms " projected from the active 

 wire on to the different portions of the plates could be 

 compared. A measure of those under! ected by the electric 



* We propose to use this term for brevity, to denote the matter which 

 recoils as the result of a radioactive process. 



