Custom House, the motions of this janitor seem to have attracted his eye without their character or purpose reaching his apprehension, and on a sudden he began to imitate his gestures as a recruit does those of his drill serjeant.  The porter having drawn up in front of the door, presented his staff as a soldier does his musket.  The Commissioner, raising his cane and holding it with both hands by the middle, returned the salute with the utmost gravity.  The inferior officer, much annoyed, levelled his weapon, wheeled to the right, stepping a pace back to give the Commissioner room to pass, lowering his staff at the same time in token of obeisance.  Dr. Smith, instead of passing on, drew up on the opposite side and lowered his cane to the same angle.  The functionary, much out of consequence, next moved upstairs with his staff upraised, while the author of the Wealth of Nations followed with his bamboo in precisely the same posture, and his whole soul apparently wrapped in the purpose of placing his foot exactly on the same spot of each step which had been occupied by the officer who preceded him.  At the door of the hall the porter again drew off, saluted with his staff, and bowed reverentially.  The philosopher again imitated his motions, and returned his bow with the most profound gravity.  When the Doctor entered the apartment the spell under which he seemed to act was entirely broken, and our informant, who, very much amused, had followed him the whole way, had some difficulty to convince him that he had been doing anything extraordinary."[287]

This inability to recollect in a completely waking state what had taken place during the morbid one separates this story from all the rest that are told of Smith’s absence of mind.  For his friends used always to observe of his fits of abstraction what a remarkable faculty he possessed of recovering, when he came to himself, long portions of the conversation that had been going on around him while his mind was absent.  But here there is an entire break between the one state and the other; the case seems more allied to trance, though it doubtless had the same origin as the more ordinary fits of absence, and, like them, was only one of the penalties of that power of profound and prolonged concentration to which the world owes so much; it was thinker’s cramp, if I may use the expression.  In one way Smith took more interest in his official work than ordinary Commissioners would do, because he found it useful to his economic studies.  In 1778 he wrote Sir John Sinclair, who had desired a loan of the French inquiry entitled Memoires concernant les Impositions, that “he had frequent occasion to consult the book himself both in the course of his private studies and in the business of his present employment,” and Sir John states that Smith used to admit “that he derived great advantage from the practical information he derived by means of his official situation, and that he would not have otherwise known or believed how essential practical knowledge was to the thorough understanding of political subjects."[288] This is confirmed by the fact that most of the additions and corrections introduced into the third edition of the Wealth of Nations—­the first published after his settlement in the Customs—­are connected with that branch of the public service.