considerable fullness; and chapters on The Self, Habit, and Character; Children's Instincts and Plays; Manners and Morals; Normals and Abnormals; and Stages of Growth, Fatigue Point, etc., follow. A very satisfactory bibliography is appended. _The Discharge of Electricity through Gases_[42] is an expansion of four lectures given by the author, Prof. _J.J. Thomson_, of the University of Cambridge, at Princeton University in October, 1896. Some results published between the delivery and printing of the lectures are added. The author begins by noticing the contrast between the variety and complexity of electrical phenomena that occur when matter is present in the field with their simplicity when the ether alone is involved; thus the idea of a charge of electricity, which is probably in many classes of phenomena the most prominent idea of all, need not arise, and in fact does not arise, so long as we deal with the ether alone. The questions that occur when we consider the relation between matter and the electrical charge carried by it--such as the state of the matter when carrying the charge, and the effect produced on this state when the sign of the charge is changed--are regarded as among the most important in the whole range of physics. The close connection that exists between chemical and electrical phenomena indicates that a knowledge of the relation between matter and electricity would lead to an increase of our knowledge of electricity, and further of that of chemical action, and, indeed, to an extension of the domain of electricity over that of chemistry. For the study of this relation the most promising course is to begin with that between electricity and matter in the gaseous or simpler state; and that is what is undertaken in this book. The subject is presented under the three general headings with numerous subheadings of The Discharge of Electricity through Gases, Photo Electric Effects, and Cathode Rays.