This paper argues for a clearer distinction between the regimes of observation established in astronomical and physical observatories in the mid-19th century. Although both observatories often shared the same spaces, directors, and techniques—such as the mechanization of observations—they studied phenomena characterized by fundamentally different temporal structures. Astronomers primarily carried out observations of phenomena with highly predictable patterns, requiring fixed and regular times of observation, whereas meteorological and magnetic observations focused on irregular and unpredictable phenomena, demanding constant, hourly observations day and night.