Long ago my pupil and I remarked that some substances such as amber, glass, and wax, when well rubbed, attracted straws, while others did not. We accidentally discover a substance which has a more unusual property, that of attracting filings or other small particles of iron from a distance and without rubbing. How much time do we devote to this game to the exclusion of everything else! At last we discover that this property is communicated to the iron itself, which is, so to speak, endowed with life. We go to the fair one day [Footnote: I could not help laughing when I read an elaborate criticism of this little tale by M. de Formy. "This conjuror," says he, "who is afraid of a child's competition and preaches to his tutor is the sort of person we meet with in the world in which Emile and such as he are living." This witty M. de Formy could not guess that this little scene was arranged beforehand, and that the juggler was taught his part in it; indeed I did not state this fact. But I have said again and again that I was not writing for people who expected to be told everything.] and a conjuror has a wax duck floating in a basin of water, and he makes it follow a bit of bread. We are greatly surprised, but we do not call him a wizard, never having heard of such persons. As we are continually observing effects whose causes are unknown to us, we are in no hurry to make up our minds, and we remain in ignorance till we find an opportunity of learning. When we get home we discuss the duck till we try to imitate it. We take a needle thoroughly magnetised, we imbed it in white wax, shaped as far as possible like a duck, with the needle running through the body, so that its eye forms the beak. We put the duck in water and put the end of a key near its beak, and you will readily understand our delight when we find that our duck follows the key just as the duck at the fair followed the bit of bread. Another time we may note the direction assumed by the duck when left in the basin; for the present we are wholly occupied with our work and we want nothing more.