But the partial exercise of the mental faculties, embraced in the act of meditation, not only disproportionately develops the cerebral organs; but deranges those which it labors to keep in incessant activity. A period of rest after labor is indispensable to the maintenance of the health and vigor of the cerebral organs. Exercise increases the flow of blood to their parts; repose, by inducing the process of recuperation, not only restores their vigor but increases their healthy volume. The invigorating effect of sleep is derived from the profound slumber into which all the faculties are calmed, except those whose functions are destined to recuperate and vitalize the entire system. To labor to keep the meditative faculties in constant action is to interrupt the process of recuperation; and, consequently, to prevent them from becoming vitalized. The man who attempts to lift a weight beyond the capacity of his muscular vigor, may never afterward be enabled to raise the tenth part of what was within his former ability; and Sir Isaac Newton, whose powers of contemplation seemed almost superhuman, after he had enervated his facilities by impelling them to constant and excessive exercise, has furnished the world with an illustration of the imbecility it engendered, by his works on the prophecies. But the principle of self-preservation inherent in the human mind, rebels against the destruction of its faculties. Habitually to exercise the contemplative faculties on one class of objects is a superhuman task. In spite of resistance the blood will pursue its natural course to the different organs of the brain, and by virtue of this fact, in conjunction with the natural condition of the system, instinct will prompt, thought intrude, emotion arise, appetite crave, passion yearn, distraction ensue; and under the external semblance of sanctity, a moral volcano will burn and heave. We may, by means of the theological subterfuge that the involuntary actions of the cerebral functions are the suggestion of impure and malignant fiends, apologize to our conscience for the intrusion of profane and worldly thoughts, but this device will not exorcise them. We shall find that in the effort to become automata, we are men; and that in the attempt to exercise one class of faculties and to concentrate: them perpetually on one class of objects, we have grappled with a giant, over whom, if we triumph it will be in our death-struggle. It is impossible to think and feel by rule. Neither particular trains of thought, nor particular kinds of emotion are at the command of the will. Belief or unbelief, the sensations of contrition, of devotion, of hope, or any other sentiment or feeling can no moro be created by an act of volition, than can storms and earthquakes.. There is a secret power acting on the nervous system, over which the will has no control.