 A series of four lectures, given by Thomson on a visit to Princeton University in 1896, were subsequently published as "Discharge of electricity through gases" (1897).Thomson also presented a series of six lectures at Yale University in 1904.Several scientists, such as William Prout and Norman Lockyer, had suggested that atoms were built up from a more fundamental unit, but they envisioned this unit to be the size of the smallest atom, hydrogen.