nd the alpha rays.

The emanation is certainly composed of alpha ions with a few molecules
agglomerated round them. Professor Rutherford has, in fact,
demonstrated that the emanation is charged with positive electricity;
and this emanation may, in turn, be destroyed by giving birth to new
bodies.

After the loss of the atoms which are carried off by the radiation,
the remainder of the body acquires new properties, but it may still be
radioactive, and again lose atoms. The various stages that we meet
with in the evolution of the radioactive substance or of its
emanation, correspond to the various degrees of atomic disaggregation.
Professors Rutherford and Soddy have described them clearly in the
case of uranium and radium. As regards thorium the results are less
satisfactory. The evolution should continue until a stable atomic
condition is finally reached, which, because of this stability, is no
longer radioactive. Thus, for instance, radium would finally be
transformed into helium.[40]

[Footnote 40: This opinion, no doubt formed when Sir William Ramsay's
discovery of the formation of helium from the radium emanation was
first made known, is now less tenable. The latest theory is that the
alpha particle is in fact an atom of helium, and that the final
transformation product of radium and the other radioactive substances
is lead. Cf. Rutherford, op. cit. passim.--ED.]

It is possible, by considerations analogous to those set forth above
in other cases, to arrive at an idea of the total number of particles
per second expelled by one gramme of radium; Professor Rutherford in
his most recent evaluation finds that this number approaches 2.5 x
10^{11}.[41] By calculating from the atomic weight the number of atoms
probably contained in this gramme of radium, and supposing each
particle liberated to correspond to the destruction of one atom, it is
found that one half of the radium should disappear in 1280 years;[42]
and from this we may conceive that it has not yet been possible to
discover any sensible loss of weight. Sir W. Ramsay and Professor
Soddy attained a like result by endeavouring to estimate the mass of
the emanation by the quantity of helium produced.

[Footnote 41: See _Radioactive Transformations_ (p. 251). Professor
Rutherford says that "each of the alpha ray products present in one
gram of radium product (_sic_) expels 6.2 x 10^{10} alpha particles
per second." He also remarks on "the experimental difficul