thomson next tried to prove the hypothesis that cathode rays carried a negative charge. In May-June 1897, he tried to deflect the rays with an electric field. Other physicists before Thomson had attempted to use the same method to bend cathode rays,
but all of them had failed. Thomson believed this was because the tube contained traces of gas. He constructed a slightly modified cathode ray tube with nearly all of the gas extracted from the tube, creating an almost perfect vacuum