Thoughts about the night are strung along the Principles of Psychology. James is concerned here, and also in the Varieties of Religious Experience, with stimuli, sensation, perception, and the imagination. Thoughts about night in the PP make reference to the quiet ticking of clocks in the house and other shifts in sensorial attention. Knowing that the task is impossible, James wants to trace the origin or cause of our mental states and impressions, including religious and spiritual ones, in particular those relating to the reality of the unseen. In both the PP and Varieties, The night is a time of stillness and also nightmares.
There is no illumination to reveal these paths. In relation to night, these are the final words of vol. 2 that conclude the PP as a whole
The causes of our mental structure are doubtless natural, and connected, like all our other peculiarities, with those of our nervous structure. ur interests, our tendencies of attention, our motor impulses, the aesthetic, moral, and theoretic combinations we delight in, the extent of our power of apprehending schemes of relation, just like the elementary relations themselves, time, space, difference and similarity, and the elementary kinds of feeling, have all grown up in ways of which at present we can give no account. Even in the clearest parts of Psychology our insight is insignificant enough. And the more sincerely one seeks to trace the actual course of psychogenesis, the steps by which as a race we may have come by the peculiar m ental attributes which we possess, the more clearly one perceives “the slowly gathering twilight close in utter night.”