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In May–June 1897, Thomson investigated whether or not the rays could be deflected by an electric field. Previous experimenters had failed to observe this, but Thomson believed their experiments were flawed because their tubes contained too much gas.
It is surprising to know that initially people failed to deflect the cathode ray. The mass of the electron is so small. It should be easily deflected by an electric field. The initial velocity of the electrons is not so high, right?