Cathode ray experiment is made in order to observe the action of electrons in vacuum tubes. Generally this proves that negative particles actually do exist.
In 1897, J.J. Thomson measured the ratio of the electrical charge to the mass of the electron using the vacuum tube with electrodes placed in it. Upon the application of the electrical and magnetic field, the electrons were able to pass through the vacuum tube until it reaches the fluorescent screen.
However, early physicists are not sure whether the cathode rays are the unknown "aether" or another unidentified mass. In those times, they don't know the subatomic particles yet. In 1838, Michael Faraday made a first remark in demonstrating the "negative charge" by constructing a vacuum tube where current is passed. Improvisation of the cathode tube in the next years made Thomson succeed and support the discovery of the electron.