When, by the previous preparations, it becomes strong and controlled, and has the power of finer perception, the mind should be employed in meditation. This meditation must begin with gross objects and slowly rise to finer and finer, until it becomes objectless. The mind should first be employed in perceiving the external causes of sensations, then the internal motions, and then its own reaction. When it has succeeded in perceiving the external causes of sensations by themselves, the mind will acquire the power of perceiving all fine material existences, all fine bodies and forms. When it can succeed in perceiving the motions inside by themselves, it will gain the control of all mental waves, in itself or in others, even before they have translated themselves into physical energy; and when he will be able to perceive the mental reaction by itself, the Yogi will acquire the knowledge of everything, as every sensible object, and every thought is the result of this reaction. Then will he have seen the very foundations of his mind, and it will be under his perfect control. Different powers will come to the Yogi, and if he yields to the temptations of any one of these, the road to his further progress will be barred. Such is the evil of running after enjoyments.