234 TH 3 INTELLECTUAL RISE IN ELECTRICITY. 



Porta's writing bears all the ear-marks of the compiler. 

 It is exceedingly diffuse, often self-contradictory, and the 

 same fact is repeated over and over again in different 

 guises, as if the change in form were regarded as involv- 

 ing a material change in substance. Much that is set 

 down may be laid out of sight at once, since it is merely a 

 re-statement of the discoveries of Peregrinus. The phe- 

 nomena of attraction and repulsion, the mode of determin- 

 ing the poles and the persistence of the poles in a divided 

 magnet, are all described as by Peregrinus with no material 

 variation, except that in the last-named instance Porta car- 

 ries the separation further, and finds the poles "in the 

 smallest fragments as well as in the great magnetic rock." 



It requires but little critical study of this treatise to reach 

 the conclusion that the notion of the field of force was re- 

 garded as by far the most important subject within the 

 knowledge of its writer, or more correctly, of the individ- 

 ual from whom that knowledge was acquired. It is re- 

 curred to over and over again, examined from many points 

 of view and tested in many different ways; so that we may 

 almost see the conception grow as experiment made it 

 clearer. This growth I shall now briefly trace. 



Porta, having pointed out that the magnetic virtue and 

 polarity remains, even when the stone is divided into mi- 

 nute grains, avers that when these grains are brought to- 

 gether, the strength of all will become unitary. Then he 

 says, u But what is more wonderful, although the strength 

 may be received in the middle of the stone, it is not dif- 

 fused at the middle but at the extremities of the polar lines 

 and . . . comes forth openly" Not long afterwards, we 

 encounter an experiment which consists in grinding a 

 magnet into the minutest grains and mixing it with some 

 inert white substance. Then, for the mystification of the 

 bystanders and Porta delights in that sort of thing a 

 magnet, hidden by a cloth, is brought up to the mass. At 

 once the magnet grains rush to the stone, packing them 

 selves densely 



