nder
the air a conductor and affect photographic plates. The third are very
penetrating rays, which are not deflected by electricity and which are
seemingly identical with Roentgen rays. Professor E. Rutherford has
named these rays beta (B), alpha (a), and gamma (v) rays respectively.
Of these the beta rays are deviated strongly by the magnetic field, the
alpha much less so--very slightly, in fact--while the gamma rays are not
affected at all. The action of these three different sets of rays upon
certain substances is not the same, the beta and gamma rays acting
strongly upon barium platinocyanide, but feebly on Sidot's blende,
while the alpha rays act exactly the reverse of this, acting strongly on
Sidot's blende.

If a surface is coated with Sidot's blende and held near a piece of
radium nitrate, the coated surface begins to glow. If now it is examined
with a lens, brilliant sparks or points can be seen. As the radium is
brought closer and closer these sparks increase in number, until, as Sir
William Crookes says, we seem to be witnessing a bombardment of flying
atoms hurled from the radium against the surface of the blende. A little
instrument called a spinthariscope, devised by Dr. Crookes and on sale
at the instrument and optical-goods shops, may be had for a trifling
sum. It is fitted with a lens focused upon a bit of Sidot's blende and
radium nitrate, and in a dark room shows these beautiful scintillations
"like a shower of stars." A still less expensive but similar device
is now made in the form of a microscopic slide, to be used with the
ordinary lens.

As we said a moment ago, radium appears to be an elementary substance,
as shown by its spark-spectrum being different from that of any other
known substance--the determinative test as fixed by the International
Chemical Congress. A particle of radium free from impurities should,
therefore, according to the conventional conception of an element,
remain unchanged and unchangeable. If any such change did actually take
place it would mean that the conception of the Daltonian atom as
the ultimate particle of matter is definitively challenged from a new
direction. This is precisely what has taken place. In July of 1903 Sir
William Ramsay and Mr. Soddy, in making some experiments with radium,
saw produced, apparently from radium emanations, another quite different
and distinct substance, the element helium. The report of such a
revolutionary phenomenon was naturally