If the topic be highly abstract, show its nature by concrete examples. If it be unfamiliar, trace some point of analogy in it with the known. If it be inhuman, make it figure as part of a story. If it be difficult, couple its acquisition with some prospect of personal gain. Above all things, make sure that it shall run through certain inner changes, since no unvarying object can possibly hold the mental field for long. Let your pupil wander from one aspect to another of your subject, if you do not wish him to wander from it altogether to something else, variety in unity being the secret of all interesting talk and thought. The relation of all these things to the native genius of the instructor is too obvious to need comment again. One more point, and I am done with the subject of attention. There is unquestionably a great native variety among individuals in the type of their attention. Some of us are naturally scatterbrained, and others follow easily a train of connected thoughts without temptation to swerve aside to other subjects. This seems to depend on a difference between individuals in the type of their field of consciousness. In some persons this is highly focalized and concentrated, and the focal ideas predominate in determining association. In others we must suppose the margin to be brighter, and to be filled with something like meteoric showers of images, which strike into it at random, displacing the focal ideas, and carrying association in their own direction. Persons of the latter type find their attention wandering every minute, and must bring it back by a voluntary pull. The others sink into a subject of meditation deeply, and, when interrupted, are 'lost' for a moment before they come back to the outer world.