Earth Study 841 



1 1 . Try this same experiment by thrusting the needles through the top 

 of a cork and float them on a pan of water. Do the north poles of these 

 needles attract or repel each other? Do the south poles of these needles 

 attract or repel each other? If you place the north pole of one needle at 

 the south pole of the other do they join and make one long magnet pointing 

 north and south ? 



12. Take a pocket compass; place the north end of one of the mag- 

 netized needles near the north arm of the compass needle ; what happens ? 

 Place the south pole of the needle near the north arm of the compass needle, 

 what happens? Can you tell by the action of your magnet upon the 

 compass needle which end of your magnet is the north pole and which the 

 south pole ? 



13. Magnetize several long sewing needles by rubbing some of them 

 toward the eye with the magnet and some from the eye toward the point. 

 Take some small corks, cut them in cross sections about one-fourth inch 

 thick, thrust a needle down through the center of each leaving only the eye 

 above the cork. Then set them afloat on a pan of water. How do they 

 act toward each other? Try them with a bar magnet first with one end 

 and then with the other, how do they act ? 



14. Describe how the needle in the mariner's compass is used in 

 navigation. 



I s . Place fine iron filings on a pane of glass or on a stiff paper. Pass a 

 magnet underneath; what forms do the filings assume? Do they make a 

 picture of the direction of the lines of force which come from the magnet ? 

 Describe or sketch the direction of these lines of force, when the poles of a 

 horseshoe magnet are placed below the filings. Place two similar poles of a 

 bar magnet beneath the filings ; what form do they take now ? 



16. What is lodestone? Why is it so called ? 



17. What is the difference between lodestone and a bar magnet? What 

 is an electro magnet? 



18. Write an English theme on "The Discovery and Early Use of the 

 Mariner's Compass." 



Supplementary reading — Electrical Experiments, Bonney; The Wonder 

 Book of Magnetism, Houston ; ' 'The Third Royal Calendar" from Arabian 

 Nights Entertainments. 



"Now, chief of all, the magnet's power I sing. 

 And from what laws the attractive functions spring; 

 The magnet's name the observing Grecians drew 

 From the magnetic regions where it grew; 

 Its viewless potent virtues men surprise, 

 Its strange effects they view with wondering eyes. 

 When, without aid of hinges, links, or springs, 

 A pendant chain we hold of steely rings 

 Dropt from the stone — the stone the binding source, — • 

 Ring cleaves to ring, and owes magnetic force: 

 Those held superior, those below maintain. 

 Circle 'neath circle downward draws in vain, 

 Whilst free in air disports the oscillating chain." 



— "De Rerum Naturae," Lucretius, 93-52 B. C. 



