
210 RADIO-ACTIVE EMANATIONS [ CH. 
When a few centigrams of moist radium bromide were placed on a 
screen, any slight motion of the air caused the luminosity to move 
to and fro on the screen. The direction of phosphorescence could 
be altered at will, by a slow current of air. The effect was still 
further increased by placing the active material in a tube and 
blowing the air through it towards the screen. A screen of barium 
platimo-cyanide or of Balmain’s paint failed to give any visible 
hight under the same conditions. The luminosity was not altered 
by a magnetic field, but it was affected by an electric field. If the 
screen were charged the luminosity was more marked when it was 
negative than when it was positive. 
Giesel states that the luminosity was not equally distributed, 
but was concentrated in a peculiar rmg-shaped manner over the 
surface of the screen. The concentration of luminosity on the 
negative, rather than on the positive, electrode is probably due to 
the excited activity, caused by the emanation, and not to the 
emanation itself. This excited activity (see chap. IX) im an electric 
field is concentrated chiefly on the negative electrode. The 
electric field, probably, does not act on the emanation itself but 
concentrates the excited activity, due to the emanation present, on 
to the negative electrode. 
An experiment to illustrate the phosphorescence produced in 
some substances by the rays from a large amount of emanation is 
described in section 160. 
139. Curie and Debiernet have made an examination of the 
emanation from radium, and the excited activity produced by it. 
They have examined the emanation given off from radium under 
very low pressures. The tube containing the emanation was ex- 
hausted to a good vacuum by a mercury pump. It was observed 
that a gas was given off from the radium which produced excited 
activity on the glass walls. This gas was extremely active, and 
rapidly affected a photographic plate through the glass. It caused 
fluorescence on the surface of the glass and rapidly blackened it, 
and was still active after standing ten days. When spectroscopi- 
cally examined, this gas did not show any new lines, but gene- 
rally those of the spectra of carbonic acid, hydrogen, and mercury. 
1 C. R. 132, pp. 548 and 768, 1901. 
