352 THE INTELLECTUAL RISE IN ELECTRICITY. 



fered from Porta, who had insisted that the diffused virtue 

 emanated from the two poles of the lodestone. But this 

 was one of the instances in which Gilbert allowed theory 

 rather than experiment to guide him; for, when he carried 

 his iron needle around the terrella, he saw plainly enough, 

 as Peregrinus had seen centuries before, that it never 

 pointed to the centre, except when it was exactly at the 

 poles. In fact, this was one of Peregrinus' methods of 

 finding the poles. At the equator, the needle stood at 

 right angles to this position, and between the equator and 

 the poles it assumed various inclinations to the latter. 

 Of course, a needle placed successively in different places 

 along a meridian of the terrella would map out, so to speak, 

 the direction of the lines of force from pole to pole. But 

 Gilbert did not perceive this any more than he saw the in- 

 consistency between his theory and his experiments; for 

 clearly, if the magnetic virtue emanated radially from the 

 centre of the terrella, his needle should always point to the 

 centre, and so take the same position at the equator as at 

 the poles. 



Cabseus, however, was more keenly alive to the logic 

 of the experiment, and to the fact that it was at odds 

 with Gilbert's supposition. He, in turn, moving the 

 needle in different positions along the meridian, sees it 

 gradually incline from the equator to the pole, until at last 

 it stands upright; or, starting from the pole, sees it grad- 

 ually incline in the opposite way, until at the equator it 

 has moved over a right angle. Then he goes a step, but a 

 long one, further. Instead of a single needle moved into 

 different positions, take a great many needles, he says 

 little ones, mere particles of iron, iron filings and put 

 them around the stone. Look at them ! At the equator 

 they adhere "prostrate" to the magnet, but at the poles 

 they "erect themselves like hairs." Hairs, branching and 

 curving away from the poles as starting points. What is 

 controlling them? Certainly the emanations from the 

 magnet; and, therefore, they must be showing the true 



