403. =Artificial Magnets.=--The power residing in the loadstone can be communicated readily, as you have seen, to iron and steel. Though soft iron takes the magnetic influence more readily than steel, it does not retain it as steel does, and the latter is therefore used in making artificial magnets. When a magnet imparts its magnetic influence it loses none of its own power, whether it be an original loadstone or an artificial magnet. There, are many ways of imparting magnetism permanently to steel, but I will notice only two of them. If you wish to magnetize a bar or needle pass one pole of a magnet from one end of it to the other a considerable number of times, always in the same direction. A more effectual way is to take two magnets, and, placing the south pole of one and the north pole of the other in contact over the middle of the bar or needle, draw them slowly and steadily apart toward the opposite ends. This process must be repeated several times. [Illustration: Fig. 283.] [Illustration: Fig. 284.] 404. =Horseshoe Magnets.=--One of the most common forms of the magnet is the horseshoe magnet, Fig. 283. There is a piece of soft iron attached to the end of this, held there by attraction. This is called the _armature_. So long as it is suffered to remain there it is a magnet having its _two_ poles, the north pole + being attached to the south pole - of the magnet which holds it, while the reverse is the case with its south pole. The object of the armature is to preserve the power of the instrument. Indeed it is found that the exertion of the magnet's power not only preserves but actually increases it. If you attach, therefore, to a magnet an armature having a hook, as seen in Fig. 284, you can add to the weight gradually from day to day, and so considerably augment the power of the magnet. 405. =Magnetic Needle.=--The magnetic needle is a very small magnet fixed upon a pivot. As it points north and south it is of great use to the mariner. The mariner's compass is a round box with such a needle balanced in it, and having a card on which is drawn a circle divided into thirty-two parts, as seen in Fig. 285. The original compass was a rude affair, consisting of a slip of loadstone laid upon a piece of cork floating in water. The date and place of its first use are unknown. [Illustration: Fig. 285.]