It seemed to Robert Acton, after Eugenia had come to his house, that something had passed between them which made them a good deal more intimate.  It was hard to say exactly what, except her telling him that she had taken her resolution with regard to the Prince Adolf; for Madame Munster’s visit had made no difference in their relations.  He came to see her very often; but he had come to see her very often before.  It was agreeable to him to find himself in her little drawing-room; but this was not a new discovery.  There was a change, however, in this sense:  that if the Baroness had been a great deal in Acton’s thoughts before, she was now never out of them.  From the first she had been personally fascinating; but the fascination now had become intellectual as well.  He was constantly pondering her words and motions; they were as interesting as the factors in an algebraic problem.  This is saying a good deal; for Acton was extremely fond of mathematics.  He asked himself whether it could be that he was in love with her, and then hoped he was not; hoped it not so much for his own sake as for that of the amatory passion itself.  If this was love, love had been overrated.  Love was a poetic impulse, and his own state of feeling with regard to the Baroness was largely characterized by that eminently prosaic sentiment—­curiosity.  It was true, as Acton with his quietly cogitative habit observed to himself, that curiosity, pushed to a given point, might become a romantic passion; and he certainly thought enough about this charming woman to make him restless and even a little melancholy.  It puzzled and vexed him at times to feel that he was not more ardent.  He was not in the least bent upon remaining a bachelor.  In his younger years he had been—­or he had tried to be—­of the opinion that it would be a good deal “jollier” not to marry, and he had flattered himself that his single condition was something of a citadel.  It was a citadel, at all events, of which he had long since leveled the outworks.  He had removed the guns from the ramparts; he had lowered the draw-bridge across the moat.  The draw-bridge had swayed lightly under Madame Munster’s step; why should he not cause it to be raised again, so that she might be kept prisoner?  He had an idea that she would become—­in time at least, and on learning the conveniences of the place for making a lady comfortable—­a tolerably patient captive.  But the draw-bridge was never raised, and Acton’s brilliant visitor was as free to depart as she had been to come.  It was part of his curiosity to know why the deuce so susceptible a man was not in love with so charming a woman.  If her various graces were, as I have said, the factors in an algebraic problem, the answer to this question was the indispensable unknown quantity.  The pursuit of the unknown quantity was extremely absorbing; for the present it taxed all Acton’s faculties.