50 THE INTELLECTUAL RISE IN ELECTRICITY. 



now, the same or north pole of a second lodestone were 

 brought up to the lower part of that last ring, then that 

 ring would be repelled and "jump up "exactly as Lu- 

 cretius says. 



Even more remarkable than this is his statement that 

 iron filings u will rave within brass basins" when the 

 stone is placed beneath. This was the first perception of 

 the field of force about a magnet by noting not merely the 

 effect of its attraction or repulsion exerted upon the pole 

 of another magnet brought into it, but upon loose iron 

 filings free to dispose themselves therein along the lines 

 of force. Then, under the astonished gaze of the poet, 

 the particles of metal arranged themselves in the curious 

 curves of the magnetic spectrum, and rose like bristles in 

 front of the poles. And as he moved the stone beneath 

 the brass basin which held them, he saw them fly from one 

 side of it to the other, sometimes grouping themselves for 

 an instant in dense bunches, then leaping apart and scat- 

 tering all so incoherently and so wildly, that it is small 

 wonder that he regarded them as raving in their frantic 

 desire to break away from the mysterious force. We 

 shall find the performances of these raving iron filings 

 astonishing the philosophers of the sixteenth century and 

 remaining always a puzzle until Faraday and Maxwell 

 found the key to it within our own time. 



The explanation which Lucretius gives of magnetic at- 

 traction is repeated by Plutarch 1 who wrote a hundred and 

 fifty years later and who applies it also to the amber attrac- 

 tion. He says, "that amber attracts none of those things 

 that are brought to it, any more than the lodestone. That 

 stone emits a matter which reflects the circumambient air 

 and thereby forms a void. That expelled air puts in mo- 

 tion the air before it, which making a circle returns to the 

 void space, driving before it towards the lodestone, the 

 iron which it meets in its way." He then proposes a 



Plutarch : Platonic Quaest., torn. 2. 



