After considering Electricity, it is not impossible to approach the study of Magnetism, and even to construct a mariner’s compass. We shall find the method of doing so by borrowing an interesting passage from the “_Magasin Pittoresque_.” Let us take a small cork and pass through it an ordinary knitting-needle (fig. 203), which we have already magnetized by placing it N.S., rubbing it gently, and always in the same direction, with one of those little iron magnets with which children amuse themselves. After the needle has been passed through the cork, we also fix into it a sewing-needle, or rather a pin, the point of which rests in one of the little holes in the upper part of the thimble. In order to balance the magnetised needle, we thrust a match into both sides of the cork, as shown in the illustration, and fasten to the ends of each a ball of wax. Thus the needle, the balls, and the pin are all balanced at once, so that the contrivance has the appearance of the illustration. As it is very important that with such a sensitive instrument any agitation of the air should be avoided, the thimble must be placed at the bottom of a common earthen pan, B D T, which should be covered over with a piece of glass, V. To graduate the compass a circle is described on a piece of paper. On this dial we trace the divisions sufficiently close only at the north extremity of the needle, and the paper is fixed underneath, as in fig. 203. Then we fix a piece of wax at the end of the match pointing N., opposite the northern extremity of the needle inside the basin. In this way we have a very useful and inexpensive compass. We may also magnetize a fine sewing-needle, and grease it by rubbing it with a little suet. It is then capable of floating on the surface of water running in the direction of the north pole. We might go on multiplying indefinitely examples of physical experiments without apparatus, but we have probably already given a sufficient number to aid our readers in imagining others. We have now in a simple manner shown how we can easily produce electricity. We may understand that electrical phenomena are produced—(1) friction between different bodies; (2) by placing bodies which differ in contact; (3) by the transition of bodies from one condition to another; (4) by chemical changes; (5) by animals. The two first, and the fourth, are the most usual causes.