- A SKEPTICs GUIDE - A SKEPTICs GUIDE 
It was found that negatively charged particles called ``cathode rays'' could be coaxed out of a hot metal filament by a large enough electric potential and accelerated to hit a screen covered with phosphorescent material where they made a bright spot [the forerunner of today's cathod ray tubes or CRT's], but until 1897 no one knew much about the properties of these particles. In that year Joseph John Thomson used magnetic deflection (the LORENTZ FORCE) to determine the charge-to-mass ratio q/m of the cathode rays.23.3 He found an astonishingly large negative ratio: q/m = -1.76 x 1011 coulombs/kg, indicating that the ELECTRON (as the ``cathode ray'' particle soon came to be known) must be a very light particle (mass me) with a very large electric charge (q = -e) where the ``electronic charge'' e was thought until recently to be the QUANTUM of electric charge - i.e. the irreducible minimum nonzero quantity of electric charge, in integer multiples of which all larger charges must come.23.4