Thus in many fairly independent ways we are brought around to this same
idea of a common structure underlying all the many seeming diversities
manifested by what we call matter.

The phenomena of radioactivity were discovered accidentally in 1896 by
the French chemist Becquerel. Many investigators immediately began
working along this promising line, and two years later Madam Curie, in
association with others, discovered the new element radium. Soon it was
discovered that radium and several other substances are continually
giving off radiations at an enormous rate, that no change of chemical
combination, no physical change of condition appears to have the
slightest effect in slowing or increasing this discharge of emanations,
while no scientific apparatus yet devised can detect any change in the
substances left behind either in respect to weight or any other
properties as the result of these enormous losses of energy. Accordingly
some people not unnaturally were ready to draw the conclusion that those
most firmly established laws of physics and chemistry, the laws of the
conservation of energy and of matter, were overthrown by this
astonishing behavior of these newly discovered substances. However, only
a few more years of study and investigation were necessary to prove
that this last conclusion was wholly unwarranted; and to-day these laws
of the conservation of energy and of matter are more firmly established
than ever.

The thing that has gone by the board is the old idea of the atoms as the
indivisible and irreducible minima of the material universe. For not
only do all the radioactive substances give off particles of helium gas
positively electrified, but _all bodies, no matter what their
composition_, can by suitable treatment, such as exposing them to
ultra-violet light, or raising them to incandescence, be made to _give