CHAP. IL] ELECTRICITY AND MAGNETISM. 



73 



iron, and, if hung up by a thread it will point north 

 and south. Figures 

 40 and 41 represent 

 a natural lodestone 

 and an artificial 

 magnet of steel, each 

 of which has been 

 dipped into iron- 

 filings ; the filings 

 are attracted and 



j, _, r Figs. 40 and 41. 



adhere in tufts. 



78. Discoveries of Dr. Gilbert. This was all, or 

 nearly all, that was known of the magnet until 1600, 

 when Dr. Gilbert published a large number of magnetic 

 discoveries in his famous work De Magnete" He 

 observed that the attractive power of a magnet appears 

 to reside at two regions, and in a long-shaped magnet 

 these regions, or poles, are usually at the ends (see Figs. 

 40 and 41). The portion of the magnet which lies be- 

 tween the two poles is apparently less magnetic, and 

 does not attract iron-filings so strongly ; and all round 

 the magnet, halfway between the poles, there is no 

 attraction at all. This region Gilbert called the equator 

 of the magnet, and the imaginary line joining the poles 

 he termed the axis. 



79. Magnetic Needle. To investigate more fully 

 the magnetic forces a magnetic needle is employed. 

 This consists (Fig. 42) of a light needle cut out of steel, 

 and fitted with a little cap of brass, glass, or agate, by 

 means of which it can be hung upon a sharp point, so 

 as to turn with very little friction. It is made into a 

 magnet by being rubbed upon a magnet ; and when 

 thus magnetised will turn into the north -and -south 

 position, or, as we should say, will set itself in the 

 "magnetic meridian" (Art. 136). The compass sold 

 by opticians consists of such a needle balanced above a 

 card marked with the " points of the compass." 



