Who discovered `e//m` for electron ? And how ?

Explanation

J.J. Thomson measured the ratio of electrical charge (e ) to the mass of electron `(m_(e ) )` by using cathode ray tube and applying electrical and magnetic field perpendicular to each other as well as to the path of elements
R.a. Milikan (1868 - 1953) devised a method known as oil drop experiment (1906 -1914) to detemine the charge on the electron.