GILBERT'S ELECTROSCOPE. 303 



straws and chaff, but metals, woods, leaves, stones, earths, 

 even water and oil "everything which appeals to the 

 senses" provided it be not aflame or in a too rarefied 

 state. He is working from the vantage-ground of the 

 isolated facts observed by others, and thus he moves be- 

 yond the implication of Fracastorio that the amber attracts 

 only "hairs and twigs," and incidentally seizes a con- 

 genial opportunity to anathematize Alexander of Apro- 

 diseus for drawing an absurd conclusion to the effect that 

 the resin exercises an occult selection in attracting only 

 the stalks and not the leaves of the garden- basil. In like 

 manner he passes beyond the bounds of Cardan's discovery 

 that the amber attraction may be cut off, and shows that a 

 screening effect happens on the interposition of moist 

 breath, a current of humid air, a sheet of paper, water, 

 linen cloth, and the silk gauze known as "sarsnet." 



He is not satisfied with merely stating that he has 



GILBERT'S ELECTROSCOPE. 1 



proved all this by actual experiment. So anxious is he to 

 avoid even the appearance of the prevailing mysticism, so 

 careful to forestall any possible charge of concealing his 

 mode of operating, so Faraday-like in his desire to leave 

 behind him his ladder for the use of others to come, that 

 he invites a repetition of his tests and a reverification of 

 conclusions, and describes the simple apparatus which he 

 has employed. He calls it a versorium in modern terms 

 it is an electroscope made of a light metal rod centrally 

 poised on an apex like the needle of a compass. It turns 

 to the rubbed electric when the latter is brought near its 



1 From the first edition of Gilbert's treatise De Magnete. 



