It may be observed that only one particle, that one
which the mentioned condition is fulfilled, keeps on moving without
any deviation. This result is used to build up a velocity selector.
By means of an experience basically similar to the previous simulation, Thomson was able to measure the ratio q/m for what he named "cathodic corpuscles". He obtained a value around 1.7 E 11 C/Kg. This happened to be the discovery of the first known subatomic particle: the electron.