4 Britain's Heritage of Science 



the pole star, but downwards, and in 1576 he measured 

 the angle between the horizontal and the direction of the 

 magnetic needle, which we now call the magnetic dip, and 

 found it to be nearly 72 in London. Such was the know- 

 ledge at Gilbert's disposal when he began his celebrated 

 researches. The word " loadstone " for the magnetic mineral, 

 derived from lead-stone, indicates how the main interest in 

 magnetic properties had been concentrated in their use for 

 purposes of navigation. Gilbert's object, on the other 

 hand, was chiefly scientific. The high position which he 

 occupies in the history of science is not merely due to his 

 discoveries, but to a great extent on his being the first man 

 of science who gave effect to Roger Bacon's teaching, 

 possessing the power and will to draw logical conclusions 

 from his experiments, and to verify by new experiments 

 the wider views suggested by these conclusions. 



Mapping out the directions in which a freely suspended 

 magnetic needle sets at different points on the earth's 

 surface, it appears to us a simple matter to infer that the 

 earth as a whole behaves like a huge magnet. A diagram 

 seems to be all that is required to complete the deduction. 

 But the world at the time was not accustomed to logical 

 reasoning of this kind. It was necessary, therefore, to 

 enforce conviction by corroborative evidence, which Gilbert 

 supplied, showing that the earth, so far as could be tested, 

 possessed all the properties of a magnet. He pointed out 

 that rods of iron lying about become magnetic under its 

 influence, just as when placed near magnetized iron, and 

 he noted that the effect is the stronger the more nearly 

 the direction of the rods coincides with the direction in 

 which a suspended needle comes to rest. Gilbert further 

 constructed a" magnetic sphere, and suspending small 

 .magnets by thin fibres, he examined how these set in 

 different directions at different points on the sphere. He 

 could thus, on a small scale, reproduce a model of the 

 earth as a magnet, and. observing that the magnetic forces 

 extend beyond the surface of his " terellum," was led to 

 speculate on the possible action of terrestrial magnetism on 

 the moon, and the mutual magnetic effects of planets on 

 each other. We readily forgive him if in these cosmic 



