MAGNETISM AND ELECTRICITY 201 



child who has a pair of magnets to play with, and to make a 

 discovery like this for one's self is really thrilling. 



If a nail or other bit of iron is brought near the end of a bar 

 magnet, it leaps toward it and is held firmly by it (Fig. Si). 

 When a second nail touches the end of the first, it is held to the 

 first, for the nail in contact with the magnet has also become a 

 magnet. So quite a chain of nails may be held by the bar 

 magnet, and a great cluster of tacks or iron filings will cling to 

 it and to each other. If you make a little paper or wooden 

 boat and put a nail in it, the magnet will draw it about when it 

 floats in a basin of water 

 even when the magnet is 

 quite a distance away, 

 for this magnetic force 

 works through paper, 

 wood, glass, or other 

 substances. 



If you lay a bar mag- 

 net down on a table with 

 a sheet of cardboard or 

 stiff paper over it, then 

 sprinkle iron filings on 

 the paper and gently tap 



the latter, the filings arrange themselves in a strange pattern 

 (Fig. 82). They seem to lie along lines of force that radiate 

 from one pole and turn around to converge at the other. If 

 a sheet of blue-print paper is used in place of ordinary paper 

 and the experiment is set in bright sunshine, when the filings 

 have arranged themselves, the peculiar design will leave its 

 shadow on the paper permanently. After the paper has stood 

 until it begins to assume a bronzed tint, take it out of the sun, 

 shake off the iron filings, and wash it in water thoroughly; then 

 pin it up to dry. The design will appear white on a blue ground. 



If a compass is set on the sheet of cardboard in the foregoing 

 experiment, its needle will assume a position parallel with the 



