In the text I have tried to show that they are always partly the creation of the imagination, and with regard to the cause explained in this quotation, it is clear that the habit of walking by night should teach us to distinguish those appearances which similarity of form and diversity of distance lend to the objects seen in the dark. For if the air is light enough for us to see the outlines there must be more air between us and them when they are further off, so that we ought to see them less distinctly when further off, which should be enough, when we are used to it, to prevent the error described by M. Buffon. [Whichever explanation you prefer, my mode of procedure is still efficacious, and experience entirely confirms it.] Accustomed to perceive things from a distance and to calculate their effects, how can I help supposing, when I cannot see, that there are hosts of creatures and all sorts of movements all about me which may do me harm, and against which I cannot protect myself? In vain do I know I am safe where I am; I am never so sure of it as when I can actually see it, so that I have always a cause for fear which did not exist in broad daylight. I know, indeed, that a foreign body can scarcely act upon me without some slight sound, and how intently I listen! At the least sound which I cannot explain, the desire of self-preservation makes me picture everything that would put me on my guard, and therefore everything most calculated to alarm me. I am just as uneasy if I hear no sound, for I might be taken unawares without a sound. I must picture things as they were before, as they ought to be; I must see what I do not see. Thus driven to exercise my imagination, it soon becomes my master, and what I did to reassure myself only alarms me more. I hear a noise, it is a robber; I hear nothing, it is a ghost. The watchfulness inspired by the instinct of self-preservation only makes me more afraid. Everything that ought to reassure me exists only for my reason, and the voice of instinct is louder than that of reason. What is the good of thinking there is nothing to be afraid of, since in that case there is nothing we can do? The cause indicates the cure. In everything habit overpowers imagination; it is only aroused by what is new. It is no longer imagination, but memory which is concerned with what we see every day, and that is the reason of the maxim, "Ab assuetis non fit passio," for it is only at the flame of imagination that the passions are kindled. Therefore do not argue with any one whom you want to cure of the fear of darkness; take him often into dark places and be assured this practice will be of more avail than all the arguments of philosophy. The tiler on the roof does not know what it is to be dizzy, and those who are used to the dark will not be afraid.