| The speculation that atoms
could not be split was called into question in
1897, when J. J. Thomson performed his famous
experiment with the cathode ray tube. This was
simply a glass tube in which most of the air was
evacuated. Thomson's setup included the typical
cathode, from which the invisible ray was emitted,
and anode. However, it also included two more
electrically charged plates, one positive and one
negative, perpendicular to the cathode ray. When
Thomson ran the experiment, the cathode ray always
deflected in the direction of the positively
charged plate, proving that the ray must consist
of negatively charged particles. Through other
experimental methods, he determined it would take
approximately 2000 of these particles to equal the
weight of one hydrogen atom. Hence, he reasoned
such particles could only come from inside the
atom. These particles are referred to as
electrons, the first subatomic particles ever
discovered. |
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