This paper utilizes Édouard Manet's work Chemin de fer, also known as Gare Saint Lazare, to discuss the concept of oeil sociologique (sociological eye). Although being selected and exposed in the Salon of 1873, Chemin de fer was very different, in subject, style and even size, from other paintings exposed in the Salon, such as that of Gérôme's Éminence grise. With an oeil sociologique, Manet saw unconsciously and spontaneously "problematic" dimensions in an ordinary scene. The picture prepares for a good start point of sociological research on railway's impact on modern life. The oeil sociologique is available only when sociological thinking emerges, in a pre-sociological stage prior to consolidation of a discipline called sociology or to initiation of a sociological study. By analyzing Chemin de fer, in accompaniment with Manet's career, I propose that period spirits, social changes and social genetics are potential factors that contribute to the oeil sociologique. Manet's case is a non-reproducible historical experiment occurred in an age when sociology was about to emerge. But the conditions and situations that contribute to Manet's oeil sociologique are heuristic for us in this age of sociology in crisis.