Discovery of Cathode Rays

It was known that when the cathode of an electric circuit was heated in a vacuum with a large potential difference applied between that cathode and the anode, a beam appeared to travel between the two electrodes. Originally this was thought to be an electromagnetic wave, and so they were called cathode rays.

J.J. Thompson (1856-1940) investigated this phenomenon and realized that these cathode rays could be deflected in their path by magnetic and electric fields. Since they carried a charge, he concluded that these rays were actually particles, which he called electrons, and was able to measure their charge-to-mass ratio.

This experimental set-up is essentially the basis for the vacuum tube, upon which early electronic devices were constructed. It also is the basis for all of our television and computer monitors (CRT - Cathode Ray Tube). It is also interesting to note that J.J. Thompson won the Nobel Prize for Physics for this discovery - for finding that electrons were particles. His son, G.P. Thompson, won the Nobel Prize a few decades later for proving that electrons were waves!!