624 Prof. Rutherford and Dr. Geiger on Transformation 



these conditions, the short-lived product of the thorium 

 emanation is concentrated on the wire. The activity of the 

 wire as it passes from the tube is examined by a zinc 

 sulphide screen placed close to it. It is seen that the 

 luminosity of the screen falls off as it is moved along the wire 

 from the end of the tube. By suitably adjusting the velocity 

 of the wire and using a long zinc sulphide screen placed 

 close to the wire the decay of the new product is very 

 strikingly and simply shown. A band of luminosity is seen 

 on the screen which decreases rapidly in intensity from the 

 point nearest the end of the tube. In order to observe a 

 similar effect with the actinium emanation, the wire must be 

 moved far more rapidly. By counting the scintillations at 

 various points along the wire it is obvious that the decay of 

 the product can be simply determined when the velocity 

 of the moving wire is known. As, however, the method is 

 similar in general principle with that employed by Moseley 

 and Fajans in the paper referred to, it has not been considered 

 necessary to give the results obtained. 



It is seen that the atoms of the new products derived from 

 the thorium and actinium emanations carry a positive charge, 

 for they are conveyed to the negative electrode in an electric 

 field. An interesting question arises whether the concentration 

 of the active deposit from these two emanations on the 

 cathode depends entirely upon the transportation of the new 

 products to the cathode and their subsequent transformation 

 in situ. For example, there is at present no certain evidence 

 of the sign or magnitude of the charge on the residual atom 

 which will result from the transformation of the new products 

 when present in the gas. This is a question of considerable 

 interest, and will be examined in detail later. The experi- 

 ments of Russ * and Kennedy t on the actinium emanation 

 have shown that under some conditions as much active 

 deposit appears on the anode as on the cathode, while in the 

 case of thorium, the active deposit under normal conditions 

 appears only on the cathode. These differences may possibly 

 receive an explanation by taking into account the difference 

 in the period of transformation of the short-lived products in 

 the two cases. Some experiments are in progress to examine 

 these points in detail. 



Nomenclature. 



The existence of two short-lived products following the 

 emanations of thorium and actinium makes a change of 



* Phil. Mag. xvii. p. 412 (1909). 

 t Phil. Mag. xviii. p. 744 (1909). 



