and Nomenclature of the Radioactive Emanations. 623 



emanation of thorium instead of actinium. For this purpose 

 a tube containing an active preparation of radiothorium and 

 mesothorium open at one end was placed at the base of the 

 vessel. The emanation diffused from the tube into the air 

 space. The increase of luminosity was relatively far more 

 marked than in the case of the actinium emanation, a result 

 probably due to the fact that a considerable fraction of the 

 actinium product was transformed before the electric field could 

 transport it to the negative electrode. A similar experi- 

 ment was performed with a vessel containing some radium 

 emanation ; but the increase of luminosity on applying the 

 field was small and the decrease of luminosity after the 

 electric field was cut off' was difficult to detect. In this case, 

 the radium A of half-value period three minutes v\as con- 

 centrated on the rod. No appreciable effect is observed 

 in any of the experiments if the central rod is charged 

 positively. 



In this connexion, it is of interest to recall an experiment 

 on the actinium emanation made many years ago by Giesel *. 

 A narrow metal tube containing a strong actinium preparation 

 at one end was placed with the open end downwards about 

 5 cm. from the surface of a zinc snphide screen. The screen 

 could be charged negatively to a high potential, and the 

 cylinder connected with earth. On applying the electric field 

 a luminous spot of light instantly appeared on the screen 

 under the tube. Giesel suggested in explanation that a new 

 type of radiation was emitted by the emanation which he 

 termed the E rays. It has been generally assumed that the 

 effect observed by Giesel was due to the concentration of 

 the ordinary actinium deposit on the zinc sulphide screen. 

 In the light of the experiments described in this paper, there 

 appears to be no doubt, however, that the luminosity was 

 initially mainly due to the very short-lived product of the 

 actinium emanation. This travelled along the lines of force 

 to the zinc sulphide screen and was transformed in situ, 

 giving rise to the luminosity observed. 



The presence of the new product in the thorium emanation 

 and its rapid decay can be simply shown in the following- 

 way. A small brass cylinder about 6 cm. long is connected 

 with a strong source of thorium preparation, and the ends 

 are closed by small ebonite corks. An endless wire, which 

 can be kept in constant movement by means of a motor, 

 passes through small holes in the ebonite stoppers. The 

 outside of the cylinder is connected with the positive pole of 

 the battery, and the wire with the negatiye pole. Under 



* Ber. d. D. Chem. Ges. xxxvi. p. 342 (1903). 



