THE ORB OF VIRTUE. 



291 



and coition the effused strengths or Forms which surround 

 the lodestone, and which illustrate Gilbert's conception of 

 the magnetic force. A more detailed examination of his 

 theory shows that he regards the force of the terrella as sent 

 out in all directions, attracting whatever iron or magnetic 

 body may come within the sphere of influence; and the 

 nearer the iron to the lodestone, the greater the force by 

 which it is drawn. The shape of the field, he thinks, con- 

 forms to that of the emitting body, and he compares its 

 physical characteristics, as Porta had already done, to 

 those of light; but he goes a step further and regards it as 

 merely soliciting bodies that are in amicable relations with 



GILBERT'S NOTION OF THE ORB OF VIRTUE AROUND THE MAGNET. 1 



itself, without actually exerting any motive energy upon 

 them. In fact, he is inclined to regard the magnetic field 

 not merely as revealed by the presence of bodies of mag- 

 netic material placed in it, but as in some way subjectively 

 connected with such bodies, preventing either the force 

 being imbibed, or given back to its original source. He 

 finds, however, that the lines of magnetic force of his ter- 

 rella are meridional and numberless, and concludes that 

 the center of the terella is the center of force, although the 



1 From the first edition of his treatise De Magnete. A is a compass 

 needle at the equator, and C another needle at the pole D. 



