78 ELEMENTARY LESSONS ON [CHAP. n. 



Nickel. Chromium. 



Cobalt. Cerium. 



Manganese, 



and a few others. But only nickel and cobalt are at all 

 comparable with iron and steel in magnetic power, and 

 even they are very far inferior. Other bodies, sundry salts 

 of iron and other metals, paper, porcelain, and oxygen 

 gas, are also very feebly attracted by a powerful magnet. 



87. Diamagnetism. A number of bodies, notably 

 bismuth, antimony, phosphorus, and copper, are repelled 

 from the poles of a magnet. Such bodies are called 

 diamagnetic bodies; a fuller account of them will be 

 found in Lesson XXVIII. 



88. The Earth a Magnet. The greatest of 

 Gilbert's discoveries was that of the inherent magnetism 

 of the earth. The earth is itself a great magnet^ 

 whose " poles " coincide nearly, but not quite, with the 

 geographical north and south poles, and therefore it causes 

 a freely-suspended magnet to turn into a north and south 

 position. The subject of Terrestrial Magnetism is 

 treated of in Lesson XII. It is evident from the first 

 law of magnetism that the magnetic condition of the 

 northern regions of the earth must be the opposite to 

 that of the north-seeking pole of a magnetised needle. 

 Hence arises the difficulty alluded to on page 75. 



89. Magnetic Induction. Magnetism may be 

 communicated to a piece of iron, without actual contact 

 with a magnet. If a short, thin unmagnetised bar of 

 iron, be placed near some iron filings, and a magnet be 

 brought near to the bar, the presence of the magnet 

 will induce magnetism in the iron bar, and it will now 

 attract the iron filings (Fig. 45). This inductive action 

 is very similar to that observed in Lesson III. to take 

 place when an electrified body was brought near a non- 

 electrified one. The analogy, indeed, goes farther than 

 this, for it is found that the iron bar thus magnetised by 

 induction will have two poles ; the pole nearest to the 



