DISCOVERY BY MEANS OF NEW OBSERVATIONS. 669 



W. Siemens was the first to discover by observation the 

 electric charge in underground telegraph wires, and during 

 the same year, Baumgartner first observed the existence 

 of earth-currents in telegraph wires. It was partly by 

 observation, that Latimer Clark, in 1852, discovered the 

 retardation of electric signals in submarine cables. 



Much of our knowledge of the science of magnetism 

 was largely acquired by the employment of the same 

 method. The Homeric poems mention the attractive 

 power of the loadstone, and the Greeks, 1,000 years before 

 Christ, are said to have obtained the stone from Magnesia, 

 in Lydia. 1 Flavio Giova, about the year 1320, has had 

 the credit given him of having been led to invent the 

 mariner's compass, in consequence of observing that a freely 

 suspended magnetised needle points north and south ; he 

 fastened the needle to a piece of cork, and floated the latter 

 upon water; but Gruiot de Provence, about the year 1200, 

 in a poem written by himself, states that prior to that 

 time, mariners used a ' touched ' needle for a compass, 

 and the Chinese are said to have employed a similar 

 instrument 1,040 years and even 2,600 years before Christ. 2 

 It was by resorting to observation that Columbus, in 

 1492, discovered the variation of the compass. The 

 Chinese, however, appear to have previously known of the 

 existence of this phenomenon ; for in a Chinese book on 

 * Natural History ' &c., published about the year 11 11 it is 

 stated : ' When a steel point is rubbed with the magnet 

 it acquires the property of pointing to the south ; yet it 

 declines always to the east, and is not due south. If the 

 needle be passed through a wick (made of a rush) and 

 placed on water, it will also indicate the south, but with a 



1 See Encyclopaedia Metropolitana, vol. iii. art. ' Magnetism, 'p. 735. 



2 Ibid. p. 736 ; also Sir W. Snow Harris's Rudimentary Magnetism, 

 parts i. and ii. pp. 1, 3, and 5 ; also "Davis, The Chinese, pp. 277, 278. 



