Before 1897, the atom model was believed to be a solid sphere. Thomson then disagreed with this idea.

He conducted an experiment by producing a visible beam called a cathode ray in a tube. He also placed two plates with opposite charges around the beam and two magnets on either side of the tube. The result showed that

• The particles are attracted by positive (+) charges and repelled by negative (−) charges ⇒ They must be negatively charged
• They exist as a part of the atom and are less massive than atoms regardless of the source material
• These subatomic particles can be found within atoms of all elements

Electrons were found like this. He later proposed that atoms can be described as negative particles floating within a soup of diffuse positive charge. The model was known as the Plum Pudding model.