368 NINETEENTH CENTURY. PT. III. 



magnetism. We have seen (p. 53) that the invention of 

 the mariner's compass in the fifteenth century arose from 

 Flavio Gioja noting that a needle which has been rubbed 

 along a piece of loadstone always points north and south. 

 But why should the needle lie in this direction? What 

 force makes it turn round when you leave it free after 

 placing it another way? Ever since the fifteenth century 

 people had asked this question, and when Volta and 

 Franklin showed that electrical currents are constantly 

 passing to and fro in our atmosphere, scientific men began 

 to consider whether it might not.be some force like elec- 

 tricity which acted upon the magnet ; especially as it had 

 been observed that when a ship was struck by lightning, 

 the needle of the mariner's compass was sometimes thrown 

 quite out of its right position. 



Still nothing was really known until the year 1819. In 

 that year, when Professor Oersted was one day making some 

 galvanic experiments at a lecture, it happened that a magnetic 

 needle poised upon a point (as in Fig. 63) was standing 

 near the wire along which an electric current was passing. 

 All at once, when the current was very strong, the needle 

 became excited and began to turn round upon the point. 

 Oersted and his assistants were much surprised at this, and 

 the consequence was that during several months Oersted 

 made a series of experiments by which he proved that an 

 electric current passing near a magnetic needle will always 

 make it turn round so as to lie ACROSS the path of the 

 current. 



For example, if the bar of copper wire a b, supported on 

 the glass rods *, ^, be so placed that the end b points to the 

 north and a to the south, then the magnetic needle c will he 

 exactly in a line with the bar, because a magnet always 

 points north and south. But if the two ends of" the coppei 



