DISCOVERIES IN MAGNETISM. 131 



It is plain that this operation must have required con- 

 siderable thought for its invention. It was necessary to 

 discover, yr^, that a lodestone bar would, when free to 

 turn, place itself longitudinally in a north and south 

 direction : second, that an artificial lodestone could be 

 made by rubbing a needle with the natural lodestone: 

 third, that such a needle would place itself north and 

 south in the same way as a lodestone : fourth, that such a 

 needle would be free to turn if floated on water: fifth, 

 that a certain end of the needle would always point to the 

 star, and that the indication of that end must be followed : 

 sixth, that, in order to make this extremity always north- 

 indicating, the needle must be rubbed with a definite part 

 of the magnet and in a definite way, that is to say, the 

 needle must be rubbed from south-pointing end to north- 

 pointing end by a certain part of the magnet, or from 

 north-pointing end to south-pointing end by an opposite 

 part of the same magnet; any departure from the foregoing 

 would make the end of the needle regarded as north- 

 pointing turn to the south, and so destroy the utility of 

 the apparatus : seventh, that the floating needle would not 

 only follow a lodestone bodily, as the iron moved over the 

 silver dish, as told by St. Augustine, but by suitably mov- 

 ing the lodestone it could be made to rotate : eighth, that 

 the inertia of the needle and the resistance of the water 

 could be first overcome artificially and the needle set in 

 motion, so that afterwards the directive force of the earth, 

 tending to set the needle in a particular position, north 

 and south, would act jointly with the inertia and the 

 liquid resistance as a force tending to stop the needle, in- 

 stead of as a force tending to set the needle in motion in 

 opposition to both of these resistances. 



This is a most extraordinary category of discoveries for 

 any period of the world's history, let alone a time when 

 physical research was impeded in every direction, and the 

 human brain supposed competent to evolve all human 

 knowledge. It includes the perception of a difference be- 



