PORTA ON THE FIELD OF FORCE. 235 



chin;" or in other words, behaving just as do the well- 

 known iron filings. (Porta sees at once the possibility of 

 drawing iron out of sand mixed with the ore by this 

 means, and mentions it.) "This shock of hairs," he says, 

 u adheres to the stone so persistently that they can hardly 

 be detached: even when the stone is struck by a hammer, 

 or two stones covered with them are nibbed together, 

 still they stick on. They stand erect like spurs, and the 

 more the stone is rubbed by another stone, the more they 

 congregate." So much Lucretius had also seen in the 

 Samothracian marvels. 



But now follows the direct recognition of the field "It 

 is to be noted that the point diffuses virtue in its sphere as 

 from centre to circumference, and just like the light of a 

 candle, which is diffused everywhere and illuminates a 

 chamber, and the further it recedes the more languidly it 

 glows; and after a little further movement, it is lost; and 

 then, as much as it approaches nearer, the more vividly it 

 shines. In the same way, this force emanates from the 

 point; and the nearer the latter, the more strongly it 

 draws, while the greater the distance the more it is remiss: 

 so that, if it recedes much, it vanishes and does nothing; 

 therefore, in place of any other term we will call the ex- 

 tent of its power 'the sphere of its virtue.' " l 



What more was there left in substance to discover as to 

 the law of magnetic attraction and repulsion? Every par- 

 ticle of matter in the universe, Newton tells us, "attracts 



1 Literal translation The English edition of Porta's Natural Magick 

 (London, 1658,) renders the passage as follows : "Giving you to under- 

 stand that the Pole sends its force to the Circumference. And as the 

 light of a Candle is spread everyway, and enlightens the Chamber; and 

 the farther it is off from it, the weaker it shines, and at too great a dis- 

 tance is lost; and the neerer it is, the more cleerly it illuminates: so the 

 force flies forth at that point ; and the neerer it is, the more forcibly it 

 attracts ; and the further off, the more faintly : and if it be set too far 

 off, it vanisheth quite, and doth nothing. Wherefore for that we shall 

 say of it, and mark it for, we shall call the length of its force the com- 

 pass of its Virtues." Note passim the old use of the English word 

 "compass" for "sphere." 



