Each
kind of charged particle produced its own parabola on
the photographic plate, and there were as many parabolae
as there were different kinds of particles. It seemed
that any gas could be made to carry a positive charge.
Thomson
realised that by measuring the tracks on the photographs
he could tell what types of gas were present in the
tube. His apparatus provided a method of chemical analysis.
In
1909 Thomson was joined by Francis Aston from Birmingham
University, and together they improved the accuracy
of Thomson's positive ray apparatus. In 1912 they found
an unusual effect while investigating neon. Neon produced
a strong trail at 20, corresponding to an ion one twentieth
the specific charge of the hydrogen ion. But this trail
was always accompanied by a second trail at 22, and
a very weak one at 11.
