Secondary Réntgen Radiation. 559 
energy of secondary radiation is proportional simply to the 
quantity of matter passed through by a primary beam of given 
intensity. Using sheets of different metals, equal weights are 
productive of a greater secondary ionization the greater the 
absorbability of this radiation by sheets of aluminium ; so 
that on the assumption that the ionizing-power varies for 
these radiations at a rate of 5 or 6 times the absorbability in 
aluminium—evidence for which I have previously given— 
the energy of radiation from equal masses is approximately 
the same in each case. As an example, the radiation from 
tin was approximately 5 times as absorbable by aluminium 
as the primary radiation, while the ionization produced in the 
secondary electroscope by this radiation was about 29 times 
the ionization produced by the secondary radiation proceeding 
from an equal mass of air. 
For the few metals experimented upon, the energy of 
secondary radiation is of the order of magnitude which would 
bring it into agreement with the law found for gases and 
light solids. Further experiments are being made to test 
this more accurately. 
It should be observed that in these measurements the 
radiation from metals which is absorbed by a few millimetres 
of air under normal conditions has not been taken account of. 
This may or may not form a part of the radiation accounted 
for by the acceleration of the negative corpuscles or electrons 
in the intense electric fields in the primary Rontgen pulses. 
Further experiments on the subject are necessary. 
The results of these experiments may be summarized thus:— 
(1) The character of secondary X-radiation from gases 
differs slightly from that of the primary producing it. (From 
air the secondary has greater ionizing power in air.) 
(2) The penetrating rays are transformed to a greater 
extent than the more absorbable rays. (See previous note.) 
(3) The energy of secondary radiation from a given gas 
through which a primary beam of given intensity is passin 
independent of the character of the primary radiation. 
(4) The energy of secondary radiation from gases and 
those light solids which are the source of a radiation differine 
little in character from the primary, is proportional to ine 
quantity of matter through whtch the primary beam of given 
intensity passes. 
(5) In the passage of X-radiation through air at 0° C. and 
76 ems. of the pressure, the diminution of intensity due to 
secondary radiation is of the order of magnitude -02 per ce 
per centimetre. 
N.B. This is.a large fraction of the total loss of intens 
due to all causes for fairly penetrating rays. 
o's 
= 1s 
nt. 
ity 
