This enthusiasm was necessary for his genius, and made it effective.
But this enthusiasm, prolonged as it often has been by the operation of the imaginative existence, becomes a state of perturbed feeling, and can only be distinguished from a disordered intellect by the power of volition possessed by a sound mind of withdrawing from the ideal world into the world of sense.

It is but a step which may carry us from the wanderings of fancy into the aberrations of delirium.

The endurance of attention, even in minds of the highest order, is limited by a law of nature; and when thinking is goaded on to exhaustion, confusion of ideas ensues, as straining any one of our limbs by excessive exertion produces tremor and torpor.
With curious art the brain too finely wrought Preys on herself and is destroyed by Thought; Constant attention wears the active mind, Blots out her powers, and leaves a blank behind-- The greatest genius to this fate may bow.
Even minds less susceptible than high genius may become overpowered by their imagination.

Often, in the deep silence around us, we seek to relieve ourselves by some voluntary noise or action which may direct our attention to an exterior object, and bring us back to the world, which we had, as it were, left behind us.

The circumstance is sufficiently familiar; as well as another; that whenever we are absorbed in profound contemplation, a startling noise scatters the spirits, and painfully agitates the whole frame.