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.  As a matter of fact neither of these students is superior to the other, but each is great in his own line.  In one set, you have an example of automatic mentation in Mathematics, Science and Geography; in the other in Literature and Art.  But suppose the first set tried to master Literature and Art and the second grappled with Mathematics and Science, each would then be practising actual concentration.  In each set the active function would be exercised and will-power would develop on both sides.  Do you see?  Occultists say that all power results from the continual exercise of active mentation and all weak-mindedness is the direct outcome of this wool-gathering, castle-building, inattentive habit which is an extension of passive mentation into useless channels of thought-force.  Conscious attention concentrates and even specializes mental energy as the sun-glass concentrates and intensifies the heat of the rays of the sun.  Focus your full attention upon the thing to be done, take a keen interest in its accomplishment to the exclusion of all else, and you will obtain wonderful results.  The man of developed, concentrative power holds in his hand the key to success, with the results that all his actions, voluntary or involuntary, are pointed to the accomplishment of his object.  Remember therefore in conclusion: