_=13. Poles; Equator.=_ The ends of a magnet are called its _poles_. The end marked with a line, or an N, should be the _north_ pole. The unmarked end is the _south_ pole. N and S are abbreviations for north and south. The central part, at which there _seems_ to be no magnetism, is called the _neutral point_ or _equator_. =EXPERIMENT 6. To ascertain the nature of substances attracted by a magnet.= _Apparatus._ The horseshoe magnet, H M (Fig. 2); silver, copper, and nickel coins; iron filings (No. 17), nails, tacks, pins, needles; pieces of brass, lead, copper, tin, etc. (Ordinary tin is really sheet iron covered with tin.) Use the various battery plates for the different metals. =14. Directions.= (A) Try the effect of H M upon the above substances, and upon any other substances thought of. _=15. Magnetic Bodies; Diamagnetic Bodies.=_ Substances which are attracted by a magnet are said to be _magnetic_. A piece of soft iron wire is magnetic, although not a magnet. Very strong magnets show that nickel, oxygen, and a few other substances not containing iron, are also magnetic. Some elements are actually repelled by a powerful magnet; these are called _diamagnetic_ bodies. It is thought that all bodies are more or less affected by a magnet. _=16. Practical Uses of Magnets.=_ Many practical uses are made of magnets, such as the automatic picking out of small pieces of iron from grain before it is ground into flour, and the separation of iron from other metals, etc. The most important uses of magnets are in the compass and in connection with the electric current, as in machines like dynamos and motors. (See experiments with electro-magnets.) =EXPERIMENT 7. To study the action of magnetism through various substances.= _Apparatus._ Horseshoe magnet, H M; a sheet of stiff paper; pieces of sheet glass, iron, zinc, copper, lead, thin wood, etc.; sewing-needle. (A tin box may be used for the iron, and battery plates for the other metals.) =17. Directions.= (A) Place the needle upon the paper and move H M about immediately under it. (B) In place of the paper, try wood, glass, etc. (C) Invent an experiment to show that magnetism will act through your hand. (D) Invent an experiment to show that magnetism will act through water. _=18. Magnetic Transparency; Magnetic Screens.=_ Substances, like paper, are said to be _transparent_ to magnetism. Iron does not allow magnetism to pass through it as readily as paper and glass; in fact, thick iron may act as a _magnetic screen_. =EXPERIMENT 8. To find whether a magnet can give magnetism to a piece of steel.=