The works of the Honourable Robert Boyle, Esq., epitomiz'd by Richard Boulton ... ; illustrated with copper plates.

EXPERIMENT VII.

TO shew that the Attraction of light Bodies, depends on very small circumstances, I made use of a Downy Feather taken off the Bo∣dy of a Fowl, to which when it had been at∣tracted by an excited piece of Amber, I appli∣ed the end of my Finger to it, upon which it stuck and left the Amber. The same success I had, when the Experiment at distinct times was tryed with the Tip of a Silver Instrument, and Iron Key, and, a piece of black Polish'd Marble. We had the like success, when the Experiment was tryed at several distant times afterwards. But one thing remarkable was, that if the Am∣ber had lost it's attractive virtue, before my Finger or the other Bodies were applyed, the Feather was not disposed to stir, till the Amber was again excited.

To conclude these Notes, I shall advertise, that the event of Electrical Experiments is very uncertain, and varied by slight Circum∣stances, some of which are altogether over∣look'd, which in some Measure appears from the above recited Notes.

And therefore I shall add, that sometimes it is very hard to know whether a Body be Electri∣cal

or not; for, tho' Kircher denies Chrystal to have an attractive power; yet I have observ'd the contrary. And tho', the industrious Gilbert denies Electricity to Cornelians and Emeralds, yet all that I have try'd, had some Degree of it, except one Cornelian. And indeed Electrici∣ty is constantly inherent in Diamonds, so that it may be one good way to try whether they be Genuine, since most of them are considerably more attractive than common Glass. But to conclude, I shall add further, that rough Diamonds are Observ'd, to have a faculty of attracting much more eminently than Polish'd ones; for which no other Reason can be conceived, but that the Diamond in Polishing, being conside∣rably, Heated by the Mill, several and a great part of it's Electrical Effluvia are spent and fly away.