quire to be as well wip'd as chaf'd; and even good ones will have their Operation promoted by the ſame means. And this is very agreeable to our Doctrine, ſince Terſion, beſides that it is, as I have ſometimes manifeſtly known it, a kind or degree of Attrition, frees the Surface from thoſe adherences that might choak the pores of the Amber, or at leaſt hinder the emanation of the ſteams to be ſo free and copious as otherwiſe it would be.
4. 'Tis likewiſe obſerv'd, That whereas the Magnetical Steams are ſo ſubtile, that they penetrate and perform their Operation through all kind of Mediums hitherto known to us; Electrical Steams are like thoſe of ſome odoriferous Bodies, eaſily check'd in their progreſs, ſince 'tis affirm'd by Learned Writers, who ſay they ſpeak upon particular Trial, that the interpoſition of the fineſt Linnen or Sarſnet is ſufficient to hinder all the Operation of excited Amber upon a Straw or Feather
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