We must confess, with Socrates, that the extent of our knowledge is indeed but a conviction of our ignorance. The metaphor of Sir Isaac Newton, on the insignificance of his own scientific attainments, is well known. Sir Joshua Reynolds so highly appreciated perfection in his art, that he was ever discontented with his own paintings; and frequently, as I have heard, by repeated touches, destroyed the effect of a picture, which had been in its early stages beautiful. And Dr. Johnson, after astonishing the world with his perfect specimen of lexicographical composition, confessed that he “had not satisfied his own expectations.” May I add to these the frequent _discontent_ of the unrivalled Paganini? IDA. The desire of the mind is, indeed, unlimited; and when this is intense, it wishes to appropriate to itself all which it can _comprehend_. But disappointment _must_ ensue; for all wish to be the whole, when they form but a part. Thus will ever be proved the futility of _worldly_ ambition,—it is never satisfied. But the desires of religion are not a phantom, or an incubus. True devotion, which aspires to heaven, as the hart panteth for the water-brooks, will never fail. Its fervent hopes and devout prayers, we believe, will be blessed by their accomplishment. CAST. Then the visitations of the incomparable Mab are nought but the infliction of the night-mare? Gentle Master Evelyn, how should I be aweary of your philosophy, but that I am half won over to believe it true? In good faith, “The Gordian knot of it you do unloose Familiar as your garter.” EV. Then, I pray you, let me counsel you not to court such visits, dear Castaly. There is some peril in the touch both of Mab and Mara; for although rare and transient cases of night-mare excite no alarm, yet its repetition, in a severe form, is not to be slighted. It sometimes has been the forerunner of _epilepsy_; its immediate cause being obstruction to the course of the blood by which the brain especially is surcharged, and the action of the lungs and heart impeded, as we prove by the extreme labour of breathing at the time we awake. I believe that there is usually a fulness of blood, also, in the vessels of the spinal marrow; as, although nightmare may occur in the _sitting_, it is far more frequent in the _recumbent_ position. Thus the marrow is oppressed, and there is then no force transmitted by the nerves to put the muscles into action. Distention of the stomach should be prevented, as the _diaphragm_ is thus pushed up against the lungs, and the gas is accumulated in the cavity. All these conditions often occur in our waking moods, but _then_ our judgment tells us how to relieve them speedily; whereas, _in sleep_, the load accumulates. All indigestible substances, therefore, should be avoided, as nuts, cucumbers, shell-fish, &c.