The fear of the mysterious has been already touched upon, in connection with childish terrors. I believe this fear to be instinctive, and of immense historical importance. Most superstition is due to it. Eclipses, earthquakes, plagues, and such occurrences arouse it in a high degree among unscientific populations. It is a very dangerous form of fear, both individually and socially; to eradicate it in youth is therefore highly desirable. The proper antidote to it is scientific explanation. It is not necessary that everything which is mysterious at first sight should be explained: after a certain number of explanations have been given, the child will assume that there are explanations in other cases, and it will become possible to say that the explanation cannot be given yet. The important thing is to produce, as soon as possible, the feeling that the sense of mystery is only due to ignorance, which can be dispelled by patience and mental effort. It is a remarkable fact that the very things which terrify children at first by their mysterious properties delight them as soon as fear is overcome. Thus mystery becomes an incentive to study, as soon as it ceases to promote superstition. My little boy, at the age of three and a half, spent many hours in absorbed solitary study of a garden syringe, until he had grasped how the water came in and the air came out, and how the converse process occurred. Eclipses can be explained so as to be intelligible even to very tiny children. Whatever either terrifies or interests the child should be explained if it is at all possible; this transforms fear into scientific interest by a process which is entirely along the lines of instinct and repeats the history of the race.