TRANSACTIONS OF SECTION A. 395 
a and g particles, and some do not seem to emit rays at all. The a par- 
ticles for each special product are emitted with a quite definite speed, 
which is characteristic for the product. This apparently does not hold true 
for the 8 rays. The absorption curves for the 8 rays are in some cases 
ecmplex, and seem to indicate complex 8 rays; in some cases the absorption 
curves indicate cnly one type of rays. In collaboration with Dr. Lise 
Meitner, the author began, two years ago, an investigation of all the 
various B-ray products, with the view of comparing all the separate 
and single products under identical conditions. As the result they put 
forward a working hypothesis that single radio-active products emit only 
one type of radiation, either homogeneous a particles or homogeneous 
8 particles. In the view of this hypothesis all products emitting a and 
B rays or complex B rays must be complex and be separable into two 
or more single products. The working hypothesis proved fertile in the 
case of the active deposits of thorium, actinium, and radium. 
The active deposit of thorium consists of four different, single products 
Th A, B, C, D, thorium D being a new product with a life period of 
three minutes, emitting the 8 rays which formerly were attributed to Th C. 
The active deposit of actinium consists of three different single products, 
Act A, B, C, the latter having a period of 51 minutes, and emitting the 
B rays which before had been attributed to Actinium B. 
In the case of the quickly decaying active deposit of radium, we have 
apparently single 8 rays from radium B, complex ones from radium C; 
therefore radium C must be complex and consist of three products, 
onea and two 8 ray substances. It is, of course, a matter of great diffi- 
culty to separate by chemical means very quickly decaying products, and 
I have therefore made use of the ‘recoil method’ of separating radio- 
active disintegration products. The effects in the case of pure radium C 
were very weak; but this was to be anticipated supposing the a rays 
to be omitted from the rest product of radium ©. The result seems to 
show that really radium C is complex, consisting, besides the nineteen 
minutes product, of one substance of about 1-2 minutes’ period, and one 
with an even shorter life. 
But there is still a better possibility of proving the correctness of the 
hypothesis. The authors have found that radium itself emits B rays of 
a quite distinct character. 
As it has long been known that radium itself emits also a particles, 
in the view of the hypothesis radium itself must be complex and consist 
of two different products, say radium and radium X. 
Some recent experiments seem to indicate that this might be the 
case, and it looks as if radium itself emits easily absorbable 8 rays 
only, and the hypothetical substance radium X emits the well-known a 
articles. 
If further work should prove radium to be complex, there is little doubt 
that the few other radio-active transformation products which still emit 
complex rays are complex, atid therefore may be separated. We might then 
be in a position to find some relation between life periods and other 
qualities of the products and the kind and velocity of the rays the products 
emit. 
4. On the Secondary Rays excited in different Metals by Alpha Rays. 
By Professor J. C. McLennan. 
In this paper an account was given of experiments which led to the 
following concliasions :— 
I. The secondary rays emitted by a selected metal when bombarded by 
the alpha rays from polofium deposited on copper are proportional to the 
intensity of the alpha radiation. 
