The busy and active man may in some degree counteract, or what is perhaps nearer the truth, may disregard those slight disorders of frame which fix the attention of a man who has nothing else to think of; but this does not tend to prove that activity of mind will enable a man to disregard a high fever, the smallpox, or the plague.
The man who walks twenty miles with a motive that engrosses his soul does not attend to his slight fatigue of body when he comes in; but double his motive, and set him to walk another twenty miles, quadruple it, and let him start a third time, and so on; and the length of his walk will ultimately depend upon muscle and not mind.

Powell, for a motive of ten guineas, would have walked further probably than Mr Godwin, for a motive of half a million.

A motive of uncommon power acting upon a frame of moderate strength would, perhaps, make the man kill himself by his exertions, but it would not make him walk a hundred miles in twenty-four hours.

This statement of the case shews the fallacy of supposing that the person was really not at all tired in his first walk of twenty miles, because he did not appear to be so, or, perhaps, scarcely felt any fatigue himself.

The mind cannot fix its attention strongly on more than one object at once.