288 EXCITED RADIO-ACTIVITY [CH. 
Debierne! found that actinium also gave off a large amount of 
emanation, the activity of which decayed very rapidly with the 
time. At some distance from the source, the activity of the emana- 
tion fell to half value in one-and-a-half minutes. This is not very ~ 
different from the rate of decay of the activity of the thorium 
emanation, which falls to half value in about one minute. 
This emanation produces excited activity on surrounding objects, 
and at diminished pressure the emanation produces a uniform 
distribution of excited activity in the enclosure contaiming the 
emanation. No data have yet been published of the rate of decay 
of the excited activity produced by the emanation of actinium. 
Debierne observed that the distribution of excited activity was 
altered by a strong magnetic field. The experi- 
mental arrangement is shown in Fig. 55. The 
active matter was placed at IM, and two plates 
A and B were placed symmetrically with regard 
to the source. On the application of a strong 
magnetic field normal to the plane of the paper, 
the excited activity was unequally distributed 
between the plates A and B. The results showed 
that the carriers of excited activity were deviated 
by a magnetic field in the opposite sense to the 
cathode rays, v.e. the carriers were positively 
charged. In some cases, however, the opposite 
effect was obtained. Debierne considers that the excited activity 
of actinium is due to “ions activants,” the motion of which is. 
altered by a magnetic field. Other experiments showed that the 
magnetic field acted on the “ions activants” and not on the 

Fig. 55. 
emanation. 
The results of Debierne thus lead to the conclusion that the 
carriers of excited activity are derived from the emanation and are 
projected with considerable velocity. This result supports the 
view advanced in section 184 that the expulsion of « particles 
from the emanation must set the part of the system left behind in 
rapid motion. A close examination of the mode of transference of 
the excited activity by actinium and the emanation substance is 
1 C. R..136, pp. 446 and 671, 1903. 
