56 ESSEX WORTHIES. 



discussion of the differences between magnets of loadstone and 

 masses of iron the first book is brought to a close with a remarkable 

 chapter which gives the key-note to the rest of the work. Its title 

 advances the proposition that the terrestrial globe is magnetic, and is 

 a magnet. " Our new and unheard-of opinion concerning the earth " 

 is his way of emphasizing his discovery that the earth is itself also a 

 great magnet — a big loadstone : for it was by this hypothesis that he 

 proposed to explain the puzzling facts of the several variations of the 

 compass needle. It has poles, he says, not mathematical points but 

 natural terminals, and between them lies an equator, not a mathe- 

 matical circle but a natural separation between the two polar regions. 

 The whole of the remainder of the work is devoted to sustaining this 

 remarkable generalisation. 



Book II. of the volume, the longest of all the six sections, deals 

 with magnetic motions and forces. Almost immediately, however, 

 he introduces a digression upon the attractions which can be set up 

 by rubbed amber and other electric bodies, a digression which though 

 itself of immense importance has little to do with the development of 

 his theme. We will deal separately with this interpolated chapter, 

 merely observing here that he comes to the conclusion that electric 

 actions are comparable with cohesion whilst magnetic actions are 

 comparable with gravity. In his opinion the globe of the earth is 

 collected together and coheres electrically, though it is directed and 

 turned about magnetically. This obscure saying becomes more 

 intelligible by the light of later passages. The next chapters of Book 

 II. are occupied with a discussion of the opinions of philosophers 

 about the nature of magnets and the origin of magnetic attractions, 

 followed by Gilbert's own views thereon and an account of his experi- 

 ments on the effects, upon the attractive power, of varying the exter- 

 nal shape of the loadstone. Here again we meet with his spherical 

 loadstones, specially constructed for these observations. He points 

 out that iron chips and small magnets arrange themselves in particu- 

 lar directions, dipping towards the magnetic poles of the terrella, as 

 the dipping needle does towards the poles of the earth. He con- 

 ceived the magnetic power as extending within a certain limited region 

 external to the stone ; and he indicates in his simple woodcuts with 

 external curved lines the orbits of the magnetic virtue. In one 

 woodcut, here reproduced in reduced facsimile, (Fig. i), compass 

 needles are shown pointing variously over various regions of the 

 terrella. In another, (Fig. 2), the terrella is shown enclosed within a 



