Marcu 3, 1904] 
NATURE 
419 
change into other elements. The parent form dis- 
integrates and throws off a portion of its substance, 
leaving a residue which undergoes a further change 
of a like explosive character, and so on, until a form 
of matter is reached 
possible. The explosion differs 
body like fulminate of mercury 
not gather strength with the mass of 
present, but is confined entirely to the 
atoms. All the effects observable in connection with 
radio-activity are referable to the @ particles: thus 
fluorescence is excited in certain bodies by impact; the 
ionisation of a gas is brought about by the collision of 
these particles with the neutral molecules of the gas, 
whereby they are torn asunder into ions; the warmth 
of a mass of a radio-active substance is due to its 
being bombarded by its own a rays. As the process of 
disintegration continues, certain stages are reached in 
which the substances produced are of the nature of 
chemical elements, though differing from the ordinary 
conception of an element in that their existence is 
merely temporary. To these transition forms Prof. 
Rutherford and Mr. Soddy have applied the term 
““metabolons,’’ and the duration of these is a specific 
property, depending on the nature of their aggregation. 
Thorium, for example, gives off an emanation which 
changes its character in so short a time as 87 seconds; 
the form of matter to which radium owes its power of 
exciting radio-activity in other bodies endures for about 
43 minutes; that to which thorium owes a similar pro- 
perty lasts about 16 hours; the radium emanation for 
5 days 8 hours; the uninvestigated next product of the 
disintegration of thorium, called thorium X, has a life 
of 5 days tg hours; uranium X of about 4 weeks; 
polonium of 16 months; radium of 1300 years; uranium 
and thorium of about 10° years. 
The atoms 0° ordinary chemistry represent the forms 
with longest life, and they exist to-day because they 
have survived a process of evolution in which those 
physically unfit have disappeared. The transition forms 
that of a 
it does 
matter 
from 
in that 
represent the elementary forms of matter unfitted to | 
survive, but they are brought within our powers of 
knowledge because they constitute the temporary halt- 
ing places through which matter is passing in a scheme 
in which no other change is | 
individual | 
| the supposition is confirmed. 
| ever, do not behave in the same manner, the absorption 
of slow continuous evolution from the heavier to the | 
lighter forms. During the whole existence of the 
metabolon, whether long or short, it behaves like an | 
ordinary atom. No indication whatever seems to be 
given of its approaching end, but suddenly, by some 
internal cataclysm, the cause of which is at present 
almost beyond conjecture, it flies to pieces and ceases | eas : : 
_as a soldier, he went to India in 1847 as Lieutenant in 
to exist in the form previously assumed. A new world 
is thus opened out in which the atom is not the unit, 
in which the forces are not chemical, and in which 
common physical conceptions such as temperature are 
without meaning. 
The operation of separating the transition forms | 
from the parent element by chemical means does not 
in any way affect the progress of disintegration. Left 
to itself, the parent element steadily accumulates a 
fresh crop of the transition forms separated, while the | 
quantities originally separated disappear as such by 
further change. As the activity of the parent element 
recovers to its maximum or equilibrium value, that of 
the transition forms decays to zero, and the sum total. 
is always the same as if the separation had not been 
effected. On this view the products of disintegration 
during last summer, examined radium with the 
view of discovering whether or not it resolved itself 
into helium, and after weeks of waiting were able to 
establish that this is really the case. A very minute 
bubble was all that could be obtained, and its slow dis- 
appearance, probably by absorption into the glass, was 
not unexpected. Indeed, glass which has been sub- 
jected to bombardment by the « rays, when powdered 
and heated, has been shown to give off helium, so that 
All kinds of glass, how- 
in some cases being much more rapid than in others. 
Viewed in relation to their length of life, it seems 
probable that radium, actinium, and polonium are 
merely slow-changing transition forms produced in the 
disintegration of the parent element uranium. Since 
the activity of polonium decays to half value in about 
a year, it follows that its existence in pitchblende at the 
| present time is due to its continuous production in the 
mineral. Applying the same argument to radium, it 
must also be in a state of equilibrium, the amount pro- 
duced in any given time being balanced by its rate of 
decay to inferior forms in that time. The lecturer had 
endeavoured to discover whether a quantity of uranium, 
originally free from radium, would grow a crop of that 
element, but a lengthy period must elapse before a 
definite conclusion can be reached. There is also an 
unknown factor in these considerations, viz. actinium, 
and until this element has been further investigated 
even speculation must be withheld. Pushing the 
matter back to its limits, we are face to face with the 
question, How and when did the universe originate? 
According to orthodox notions, it is tending to a state 
of exhaustion in which all change must cease. If, 
however, a constructive influence is at work, ovposing 
this process, the whole system may turn out to be a 
conservative one, limited with respect neither to the 
future nor to the past, but proceeding through con- 
tinuous cycles of evolution. This would be possible if 
a gradual and continuous accretion of atomic mass 
could take place, such as that by which the stable 
elements were originally formed. At present, however, 
all such views belong to the realm of pure conjecture. 
LIEUT.-GENERAL C. A. McMAHON, F.R.S. 
HARLES ALEXANDER McMAHON, son _ of 
Captain Alexander McMahon, of the East India 
Co.’s Service, belonged to an old Irish family, and 
was born near Highgate on March 23, 1830. Educated 
the Madras Native Infantry, and served for eight years 
in the 39th Regiment. In 1856 he was appointed a 
Commissioner in the Punjab, and was engaged for 
thirty years in various districts, including Lahore. 
While politics and educational questions occupied 
much of his time, he became greatly interested in 
geology, and especially in the crystalline rocks and 
glacial phenomena of the western Himalayas. In his 
earlier work he was impressed with the intrusive 
| character of the central gneiss of the great mountain 
must have been steadily accumulating through past | 
ages, and the discovery of helium by Sir W. Ramsay | 
in 1895 Was the first definite proof that such was really | 
the case. Helium is only known in association with 
the radio-active elements, and its inert character is one 
of the reasons for supposing that it is a final product 
of disintegration. Sir W. Ramsay and Mr. Soddy, 
NO. 1792, VOL. 69] 
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range, and his enthusiasm was so aroused that he took 
the opportunity, while on furlough in 1879-80, of 
attending the courses at the Royal School of Mines, so 
as to be initiated in the latest methods of petrological 
research. Returning to India he worked with renewed 
zeal at the igneous and metamorphic rocks, and the 
results of his observations were mostly published in 
the records of the Geological Survey of India. 
In 1885 he retired from service with the rank of 
colonel, and settled in London. He had been elected 
a fellow of the Geological Society in 1878, and he now 
took an active part in the worl of the society, serving 
