1.
Cathode rays
J.J.
Thomson became the third Cavendish Professor of Experimental
Physics in 1884. One of the phenomena he studied was
the conduction of electricity through gases.
One
subject which interested Thomson was cathode rays.
These rays are emitted at the cathode, or negative terminal,
in a discharge tube. In 1879 Crookes had proposed that
the cathode rays were 'radiant matter', negatively charged
particles that were repelled from the negatively charged
cathode and attracted to the positively charged anode.
The
nature of the cathode rays was controversial. Although
Thomson thought the rays must be particles, many Europeans
thought they were an 'etherial disturbance', like light.
In Germany Hertz had observed the rays passing through
thin sheets of gold. It seemed impossible that particles
could pass through solid matter.
Hertz
had also found (wrongly) that the rays were not deflected by electric
fields. In 1897 Thomson repeated Hertz's experiment.
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