The frontiers of
the atomic systems were breaking down.
The next step was for students (notably Soddy and Rutherford) to
find that radio-activity, or spontaneous discharge out of the
atomic systems, was not confined to radium. Not only are other
rare metals conspicuously active, but it is found that such
familiar surfaces as damp cellars, rain, snow, etc., emit a
lesser discharge. The value of the new material thus provided for
the student of physics may be shown by one illustration. Sir J.
J. Thomson observes that before these recent discoveries the
investigator could not detect a gas unless about a billion
molecules of it were present, and it must be remembered that the
spectroscope had already gone far beyond ordinary chemical
analysis in detecting the presence of substances in minute
quantities. Since these discoveries we can recognise a single
molecule, bearing an electric charge.
With these extraordinary powers the physicist is able to
penetrate a world that lies immeasurably below the range of the
most powerful microscope, and introduce us to systems more
bewildering than those of the astronomer. We pass from a
portentous Brobdingnagia to a still more portentous Lilliputia.
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