who measured the value of e/m ? thomson or millikan.

In 1897, British physicist 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 electrons.

R.A. Millikan (1868-1953) devised a method known as oil drop experiment (1906-14), to determine the charge on the electrons. He found that the charge on the electron to be – 1.6 × 10^–19 C.