704 
I have come to a different view, which I think re- 
presents the facts more adequately than these others. 
I agree with Piccard in thinking that the parent 
substance of the actinium series is an isotope of 
uranium, of atomic weight 240, not genetically 
connected with it;. but differ principally in thinking 
the atomic weight of actinium is not 232, and that 
uranium Y is not the immediate parent of proto- 
actinium. 
The scheme is as follows : 



Element. Period. nS) Radiation. Wasnt 
Actino-uranium I >5 10° years 92 a 240 
Uranium Y, 25-5 hours 90 B 236 
Uranium Y, Probably very 91 B 236 
short 
Actino-uranium IT . | >2% 10® years 92 a 236 
Parent of proto- 
actinium . | >20 years 90 B 232 
Proto-actinium <1-2 10* years 91 a 232 
Actinium . ‘ F 20 years 89 8 228 
Radio-actinium, etc. 19:5 days 90 a 228 




This scheme was arrived at from a consideration 
of the periods of corresponding members of the three 
disintegration series. Successive radio-active trans- 
formations may be classed in three ways : 
(1) Four a-particles (five in the uranium series) 
follow each other without the expulsion of 
a §-particle. 
(2) An a-particle is followed by two §-particles in 
succession and then an a-particle. 
(3) An a-particle is followed successively by a 8-, 
an a-, and a f-particle. 
In the three known examples of the first type 
each product has on the average 800 times the period 
of its successor. (For the uranium series the ratio 
is 766, for the thorium 764, for the actinium 918.) 
Yet the periods of average corresponding members 
of the three series (in the order given) are in the 
proportion of 5 x 10°, 50,and 1. Now the difference in 
atomic weight between the uranium and the thorium 
series is 2 only. I have assumed that if a time ratio 
of 5x 10° to 50 corresponds to 2, a ratio of 50 to 1 
corresponds to so small a fraction as to be negligible. 
If this be justifiable the atomic weights of the thorium 
and actinium series become identical. It follows 
that actinium has an atomic weight of 228 and so 
cannot be genetically connected with uranium if a- 
and 8- be the only particles expelled in radio-active 
transformations. 
I have found interesting relations connecting the 
periods of the bodies of the second and third types of 
successive transformations, but the only thing necessary 
for the scheme to be deduced is that in both these types 
the period of the first 8-particle is greater than that of 
the second. There are in all, excluding the change, 
parent of Pa—+Pa—+Ac—+>RdaAc, ten examples of 
the second and third types known, in all of which this 
relation holds. It is consequently not unreasonable to 
suppose that the parent of proto-actinium has a longer 
period than actinium and consequently cannot be 
uranium Y. As the latter is very probably genetically 
connected with actinium, and is undoubtedly a product 
of a body of atomic number 92, it must be an isotope of 
the parent of proto-actinium probably with an atomic 
weight 4 units greater. To connect it with the 
parent of proto-actinium it is simplest to suppose 
that it is followed by a quick-changing product 
uranium Y., corresponding to uranium X,, which 
is the parent of an isotope of the original actino- 
uranium, and this immediately precedes the parent of 
actinium as shown in the table above. ; 
NO. 2795, VOL. I11] 
NATURE 
[May 26, 1923 
The scheme, so far as I am aware, does not seriously 
contravene the results of experimental work, and 
appears to be nearer what one would expect by 
analogies from the thorium and uranium series and 
the lower part of the actinium series than those 
previously proposed. None of the new proposed 
data given in the table contravene the Geiger-Nuttall 
relation. 
rules connecting the order of the atomic weights of 
isotopic a-ray and f-ray bodies with the order of 
their periods more nearly exact than hitherto they 
have appeared to be. To Fajan’s a-ray rule there 
have been hitherto three exceptions; on the new 
scheme there is only one. The two exceptions to his 
8-ray rule do not exist in the new scheme. 
Our experimental work on the relative activity 
of uranium and its products in pitchblende leads 
to a ratio in the amounts of actinio-uranium and 
uranium I in uranium of about 5 to 95. But the 
experimental results to be expected on the assumption 
that uranium II breaks up dually in this proportion 
to form the actinium and radium series lead to so 
similar a result that at present our experimental work 
is insufficiently advanced to lead to a decision. 
Mr. W. G. Guy in this laboratory has been for some 
time engaged with me in repeating Dr. O. Hahn's 
work on uranium Z as described in the latter’s 
publication of 1921, and has independently come to 
very similar results to those described in Hahn’s 
second and recent paper. He confirms Hahn’s 
important result that uranium X, breaks up dually, 
in both cases with the emission of a $-particle to 
form uranium X, and uranium Z in a ratio of about ~ 
997 to 3. He has also measured the periods of 
uranium Y, uranium Z, and uranium X, accurately, 
and finds them to be 25:5 hours, 6°69 hours, and 70°5 
seconds respectively. These agree with the published 
values. Dr. Hahn does not appear to have noticed 
that the branching ratio, which he gives as 996°5 to 
3°5, is approximately equal to the reciprocal of the 
periods of the two bodies formed. This agreement 
may be a coincidence. If it is not, it would not be 
difficult to deduce from it information which might 
throw light on the mechanism of disintegration. 
A. S. RUSSELL. 
Dr. Lee’s Laboratory, Christ Church, 
Oxford, May 3. 

Slag mistaken for a Meteorite at Quetta. 
WIDE publicity has been given in the Press to a 
story of a fall of a large meteoric mass in Quetta, 
Baluchistan Agency. 
The Geological Survey of India has always paid 
| particular attention to falls of this kind, and, within 
an hour of the receipt of the news in Calcutta, was in 
telegraphic communication with the authorities in 
Quetta, and the receipt of specimens was anxiously 
awaited. Ultimately, approximately two hundred- 
weights of material were carefully examined, and 
found ‘to be entirely a glassy slag in which were 
embedded bits of iron wire and thin iron bands. 
So far as can be judged, the sequence of events was 
as follows: A large stack of baled bhoosa (chopped 
straw) of about five hundred tons weight was fired 
by a flash of lightning during a heavy thunderstorm, 
and a mass of slag some five tons in weight was left 
A bystander suggested that this mass was. 
behind. 
of meteoric origin. 
G. H. Tripper. 

Geological Survey of India, Calcutta, 
March 11. - 
Moreover, they appear to make Fajan’s 

EEE 
