ROBERT BOYLE'S EXPERIMENTS. 419 



is somewhat troubled about it. u His nature," says 

 Humboldt, "was cautious and doubting." "Whether 

 from such experiment one may argue," he says thought- 

 fully, "that it is but, as it were, by accident that amber 

 attracts another body and not this the amber; and whether 

 these ought to make us question if electrics may with so 

 much propriety, as has been hitherto generally supposed, 

 be said to attract, are doubts that my design does not 

 here oblige me to examine." 



So Boyle went on, and added some more things to the 

 list of electrics turpentine gum, and white sapphires, 

 and English amethysts, and emerald (which Gilbert said 

 would not attract), and carnelian and various other sub- 

 stances; which merely swell the list, and are of no im- 

 portance. He comes back for a final blow at the Form 

 theory, by distilling amber to a caput mortuum and show- 

 ing that, as the attractive quality is still present, it cannot 

 be due to the "substantial Form of amber " which has 

 here thoroughly disappeared. 



Boyle's idea of electric attraction having much in com- 

 mon with the hypothesis of corporeal emanations, which 

 we have traced through different theories, it follows, of 

 course, that he did not agree with von Guericke in the 

 incorporeal nature of the expulsive force, but, on the con- 

 trary, refers to electric repulsion very much as Cabseus did 

 long before, in proof of the fact that the briskly-moving 

 steams from the electric physically drive away the at- 

 tracted bodies. But, unlike Cabaeus, he recognized the 

 specific fact of the repulsion, indeed had to do so to reach 

 the idea that the electric operated to "discharge and shoot 

 out the attracting corpuscles" which carried away the 

 chaff, although he finds it difficult to coordinate this action 

 with the attractive effect, and admits that it happens only 

 "at a certain nick of time." * 



1 Boyle : Of the Great Efficacy of Effluviums. 1673. Cap. iv. Works: 

 Birch. Lond., 1744. Vol. Hi., 323. 

 On the basis of a paragraph, which appeared in 1673, Boyle is very 



