A sharp-eyed observer, had such been present, accustomed to studying the human face and weighing motives, would have been puzzled to guess the exact nature of the feelings which Marcus entertained for the pretty, innocent young creature who sat there, always plying her little fingers at some useful work. The puzzle would have been a still greater one for Mr. Wilkeson himself. He felt a profound interest in Pet; and she it was, and not the pale mechanic or his novel machine, that led him daily up those three flights of rickety stairs to that humble room. He said to himself, and he would have said to anybody who was entitled to call upon him for an explanation, that he had always loved children, and that the beauty and goodness of this child had deeply interested him. If there was any other motive at the bottom of his heart, he studiously concealed it from himself, as he would have concealed it from all the world. During these visits, Mr. Minford pursued his work without interruption. The screens, which were at first jealously closed, were now thrown open, and the inventor sat there in full sight of his visitor, laboring at his great mechanical problem. Repeatedly he had begged of Marcus the privilege of explaining to him the principles of the machine; but that gentleman had always resolutely declined, for the reasons before stated. And he had always observed that, a few moments after such refusal, the face of the inventor would brighten up, as if with joy that he had not parted with his secret even to one who held a fifth interest in it. Of the wonderful results which the machine was sure to accomplish, Mr. Minford was never tired of talking, nor Mr. Wilkeson of hearing, although, at these times, his eyes followed the flying motions of Pet's fingers, as if they were a part of the wonder of which the inventor discoursed so glowingly. Precisely what the machine was to effect, when completed, Marcus Wilkeson would never have known, if he had been the most attentive of listeners. Mr. Minford spoke in vague, general terms, that afforded no clue to the mystery. He talked of old philosophers and mechanicians, who had failed to discover an unnamed secret of Nature, because they had no faith in its existence. Complete faith in the existence of the thing to be discovered, as well as in the ability of the searcher to find it, he regarded as indispensable conditions of an inventor's success.