622 Prof. Rutherford and Dr. Geiger on Transformation 



that an a ray product was present in the emanation which 

 had an average life of transformation not longer than 

 1/5 of a second. These conclusions have been confirmed by 

 further experiment. As in the case of the actinium emana- 

 tion the new product has a positive charge, and in an electric 

 field is deposited on the negative electrode. The period of 

 transformation, however, is much longer than that for the 

 corresponding actinium product. It is, in consequence, not 

 practicable to determine the period of transformation by the 

 method previously employed by Geiger for the short-lived 

 product of the actinium emanation. In order to determine 

 the period, weak electric fields are required, and under 

 these conditions the loss of charge of the carriers by re- 

 combination with the ions seriously complicates the deductions 

 from the experiments. In an accompanying paper, the times 

 of transformation of these new products have been determined 

 by a new and more direct method by H. Moseley and 

 K. Fajans. It will be seen that the half- value period of 

 transformation of the product in actinium is *002 second, a 

 value in good accord deduced indirectly by Geiger. The 

 corresponding half-value period for the thorium product is 

 *14 second, a value within the limit indicated by the scintil- 

 lation experiments of Geiger and Marsden. 



The presence of these new products in the emanations of 

 thorium and actinium can be simply illustrated by experiments 

 in a dark room. The emanation from a strong preparation 

 of actinium or of thorium is allowed to diffuse into a small 

 cylindrical vessel in the centre of which is fixed a metal rod 

 insulated from the cylinder by an ebonite cork. One 

 terminal of a battery of about 1000 volts is connected to the 

 rod and the other to the outside of the vessel. About one 

 centimetre of the end of the rod is coated with a layer of 

 zinc sulphide. In a dark room without an electric field, the 

 zinc sulphide is seen to glow faintly due to the a rays from 

 the emanation. When the rod is connected to the negative 

 pole of the battery, the end of the rod is seen to light 

 brightly on the instant. This is due to the concentration of 

 the short-lived product from the whole volume of the 

 emanation space on to the small negatively charged rod. 

 On disconnecting the battery the luminosity sinks instantly. 

 By alternate application and removal of the electric field at 

 rapid intervals, the luminosity is seen to rise and fall with 

 it. In the case of actinium, the effect of the ordinary active 

 deposit becomes evident after a few minutes by a slow but 

 steady increase of the residual luminosity when the field is 

 cut off. The effects are more strongly marked using the 



