30 LIGHT SCIENCE FOR LEISURE HOURS. 



The peculiarity that the magnet needle does not, 

 in general, point to the north, is the first of a series of 

 peculiarities which we now propose briefly to describe. 

 The irregularity is called by sailors the needle's varia- 

 tion, but the term more commonly used by scientific 

 men is the declination of the needle. It was probably 

 discovered a long time ago, for 800 years before our 

 era the Chinese applied the magnet's directive force to 

 guide them in journeying over the great Asiatic plains ; 

 and they must soon have detected so marked a peculi- 

 arity. Instead of a ship's compass, they made use of 

 a magnetic car, on the front of which a floating needle 

 carried a^mall figure, whose outstretched arm pointed 

 southward. "We have no record, however, of their 

 discovery of the declination, and know only that they 

 were acquainted with it in the twelfth century. The 

 declination was discovered, independently, by European 

 observers in the thirteenth century. 



As we travel from place to place, the declination of 

 the needle is found to vary. Christopher Columbus 

 was the first to detect this. He discovered it on the 

 13th of September, 1492, during his first voyage, and 

 when he was six hundred miles from Ferro, the most 

 westerly of the Canary Islands. He found that the 

 declination, which was toward the east in Europe, 

 passed to the west, and increased continually as he 

 travelled westward. 



But here we see the first trace of a yet more singu- 



