(_d_) Take a picture, representing a landscape, the interior of a building, an assembly of persons, a square, a triangle or a more complicated geometrical figure. Look at it well. Then lay it aside. Close your eyes. Reproduce the picture mentally in detail. Then repose your mind on the same image to the exclusion of all other thoughts. This is a more fixed and meditative method and will sharpen the mind wonderfully. It will also develop the power of conscious Mental Imagery. The key to Objective Concentration is _Conscious Attention_, remember. ACTIVE AND PASSIVE MENTATION. These terms imply two different distinct functions of the human mind. The active function performs the volitional, voluntary thinking. It is the conscious focusing of the mind on some mental problem. Banishing from the mind all thoughts and ideas not in harmony with your special subject of study implies Active Mentation. This function is used by the active, wide-awake man in his busy and energetic moments. It is the key to the development of Will-Power and a vigorous intellect. You are conscious of effort when you are exercising this function. The mind becomes exhausted after a great deal of such effort and cries out for rest, because conscious attention implies close concentration of thought and can be exercised only by the conscious use of Will-Power. You ought to be able to concentrate upon one subject of thought, study and observation with undivided attention and then take your mind off that subject and put it on something else, at your will. Train your mind to 'give' perfect attention to any subject you like and also to 'shut off' or inhibit all attention on that subject. The mind is a restless thing darting from one thing to another, and, like a spoilt child, tiring of continued attention. But you must, by Will-Exercise, get control over this tendency. 'Exercise develops power. Practice makes perfect.' This you must bear in mind and, by patience and perseverance, train your mind to 'pay attention' where it ought to do so and not to pay attention where it ought not to. At first your mind will rebel like an unbroken horse at the imposition of such restraint. But really all greatness results from mind-control. _Remember active mentation is conscious, deliberate concentration. Passive mentation represents automatic, involuntary thinking._ This includes the subconscious or 'habit' mind. When a certain thought-groove has been formed in your mind, energy flows into it involuntarily, _i.e._, by itself and without any conscious effort on your part. This is passive mentation. It is automatic mental activity. Take an example. Some school-boys find Mathematics, Science and Geography easy to master from the very start. They feel quite in sympathy with the teacher of Mathematics. But History and Language are their abomination. There are others who simply cannot 'take an interest' in any Mathematics but who shine brilliantly in Language, Recitation, Composition, History.