1x] EXCITED RADIO-ACTIVITY 287 
The average mobility A deduced from a large number of 
experiments was 1°3 cms. per sec. per volt per cm. for atmospheric 
pressure and temperature. This velocity is about the same as 
the velocity of the positive ion produced by Réntgen rays in air, 
viz. 137cms. per sec. The results obtained with the radium 
emanation were more uncertain than those for thorium on account 
of the distribution of some excited activity on the positive elec- 
trode. The values of the velocities of the carriers were however 
found to be roughly the same for radium as for thorium. 
These results show that the carriers of the emanation X travel 
in the gas with about the same velocity as the positive or negative 
ions produced by the radiations in the gas. This shows either that 
the emanation X becomes attached to positive ions, or that the 
emanation X itself, acquiring in some way a positive charge, forms 
a cluster of neutral molecules which travel with it. 
186. Excited activity from actinium and ‘‘ emanation 
substance.”’ Ghiesel! observed that the “emanating substance ” 
gave off a large quantity of emanation, and that this emanation 
gave rise to a type of radiation which he termed the /# rays. 
A narrow metal cylinder contaimmg the active substance was 
placed with the open end downwards, about 5cms. above the 
surface of a zinc sulphide screen. ‘The screen was charged nega- 
tively to a high potential by an electric machine, and the cylinder 
connected with earth. A luminous spot of light was observed on 
the screen, which was brighter at the edge than at the centre. A 
conductor, connected with earth, brought near the luminous spot 
apparently repelled it. An insulator did not show such a marked 
effect. On removal of the active substance, the luminosity of the 
screen persisted for some time. This was probably due to the 
excited activity produced on the screen. 
The results obtained by Giesel support the view that the 
carriers of excited activity of the “emanation substance” have a 
positive charge. In a strong electric field the carriers travel along 
the lines of force to the cathode, and there cause excited activity 
on the screen. The movement of the luminous zone on the ap- 
proach of a conductor is due to the disturbance of the electric field. 
1 Ber. deutsch. Chem. Gesell. 36, p. 342, 1903. 
