Chap. I. Purpose of this work. II. Qualifications of the experimenter. III. Characteristics of a good lodestone. IV. How to distinguish the poles of a lodestone. V. How to tell which pole is north and which south. VI. How one lodestone attracts another. VII. How iron touched by a lodestone turns towards the poles of the world. VIII. How a lodestone attracts iron. IX. Why the north pole of one lodestone attracts the south pole of another, and _vice versa_. X. An inquiry into the natural virtue of the lodestone. PART II. Chap. I. Construction of an instrument for measuring the azimuth of the sun, the moon or any star when in the horizon. II. Construction of a better instrument for the same purpose. III. The art of making a wheel of perpetual motion. An attentive reading of the thirteen chapters of this treatise of 3,500 words will show that: (1) Peregrinus assigns a definite position to what he calls the _poles_ of a lodestone and gives practical directions for determining which is north and which south. (2) He establishes the two fundamental laws of magnetism, that like poles repel and unlike poles attract each other. (3) He demonstrates by experiment that every fragment of a lodestone is a complete magnet, and shows how the fragments should be put together in order to reproduce the polarity of the unbroken stone. (4) He shows how a pole of a lodestone may neutralize a weaker one of the same name and even reverse its polarity. (5) He pivots a magnetized needle and surrounds it with a circle divided into 360 degrees. This brief summary shows the great advance made by the author on what was known about the lodestone before his time. Most of the salient facts in magnetism are clearly described and some of their applications pointed out. So thorough and complete was this apprehension and explanation of magnetic phenomena that nothing of importance was added to it for the next three hundred years. [Illustration: FIG. 2 First pivoted compass, Peregrinus, 1269]