
one RADIO-ACTIVITY OF THE ATMOSPHERE [cH. 
along with the current of air. It does not however appear that 
the ionization of the gas is In any way due to the presence of a 
penetrating type of radiation such as is emitted by the radio- 
active bodies. Le Bon (section 8) observed that quinine sulphate, 
after being heated to a temperature below the melting point and 
then allowed to cool, showed for a time strong phosphorescence 
and was able rapidly to discharge an electroscope. The discharging 
action of quinine sulphate under varying conditions has been very 
carefully examined by Miss Gates. The ionization could not be 
observed through thin aluminium foil or gold-leaf but appeared 
to be confined to the surface. The current observed by an electro- 
meter was found to vary with the direction of the electric field, 
indicating that the positive and negative ions had very different 
mobilities. The discharging action appears to be due either to an 
ionization of the gas very close to the surface by some short ultra- 
violet light waves, accompanying the phosphorescence, or to a 
chemical action taking place at the surface. 
Thus, neither phosphorus nor quinine sulphate can be con- 
sidered to be radio-active, even under the special conditions when 
they are able to discharge an electrified body. No evidence in 
either case has been found that the ionization is due to the 
emission of a penetrating radiation. 
No certain evidence has yet been obtained that any body can 
be made radio-active by exposure to Réntgen or cathode rays. 
A metal exposed to the action of Rédntgen rays gives rise to a 
secondary radiation which is very readily absorbed in a few | 
centimetres of air. It is possible that this secondary radiation 
may prove to be analogous in some respects to the a rays from 
the radio-elements. The secondary radiation, however, ceases 
immediately the Réntgen rays are cut off. Villard? observed that 
a piece of bismuth produced a feeble photographic action after it 
had been exposed for some time to the action of the cathode 
rays in a vacuum. It has not however been shown that the 
bismuth gives out rays of a character similar to those of the 
radio-active bodies. 
The existence of a very feeble radio-activity of ordinary matter 
1 Amer. Phys. Soc. Oct. 1903. 
2 Société de Physique, July, 1900. 

