Madame
Curie, the brilliant Polish Parisian, had to work for years before she
could prove to the world that such an element existed and for years
afterwards before she could get the metal out. Yet now we can all afford
a bit of radium to light up our watch dials in the dark. The amount
needed for this is infinitesimal. If it were more it would scorch our
skins, for radium is an element in eruption. The atom throws off
corpuscles at intervals as a Roman candle throws off blazing balls. Some
of these particles, the alpha rays, are atoms of another element,
helium, charged with positive electricity and are ejected with a
velocity of 18,000 miles a second. Some of them, the beta rays, are
negative electrons, only about one seven-thousandth the size of the
others, but are ejected with almost the speed of light, 186,000 miles a
second. If one of the alpha projectiles strikes a slice of zinc sulfide
it makes a splash of light big enough to be seen with a microscope, so
we can now follow the flight of a single atom.
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