In 1897, the cathode ray tube or CRT, which is now a part of most TV sets, was the last word in advanced laboratory instrumentation and TV was still 40 to 50 years in the future. At Cambridge University in England, J.J Thomson studied the rays emanating from the cathode of the CRT. Thomson measured the ratio of charge to mass (e/m) of these corpuscles of which the rays were composed. We now call them electrons. Well do his experiment, with a somewhat modified apparatus. Main parts of the apparatus electron gun consists of filament, cathode and anode. He setup the experiment in the same way as William Crookes. When the rays got emitted he measured the e/m ratio by use of magnetic and electric fields.