nine o'clock in the morning
Her absence from town , though of only a few days ' duration , freed him from the distraction which the very possibility of seeing her presented , and night after night he ascended to his watch-tower . But he presently discovered that it was one thing to take observations on Mount Hamilton , where no other claims occupied part of his time , and quite another to watch by night and teach by day . The bishop was right in saying that his chief occupation must needs be the teaching of elementary mathematics to undergraduates . For any satisfactory results , prolonged observations must be made from twilight to dawn , and such periods of wakefulness were impossible when he must present himself before a class at nine o'clock in the morning . Not that this was necessary each day . His hours were irregular , but the morning classes were sufficiently numerous to break up the continuity of his observations , and to render their results unsure . In this quandary , he ought , perhaps , to have abandoned his purpose and to have taken up some problem in pure mathematics , but here the perversity of human nature interposed .