157 



ELECTRICAL PROPERTIES OF SILK. 



THE distinction between those bodies which are 

 apable of being excited to electricity, and those 

 rhich are only capable of receiving it from the 

 thers, appears scarcely to have been even sus- 

 >ected till about the year 1729, when this great 

 iscovery was made by Mr Gray, a pensioner in 

 Charter-House. After some fruitless attempts 

 o make metals attractive by heating, rubbing, and 

 ammering, he conceived a suspicion, that, as a 

 lass tube, when rubbed in the dark, communi- 

 ated its light to various bodies, it might possibly, 

 t the same time, communicate its power of at- 

 racting to them. In order to put this to the 

 est, he provided himself with a tube three feet 

 ive inches long, and near an inch and one-fifth in 

 iameter ; the ends of the tube were stopped by 

 ork ; and he found that, when the tube was ex- 

 ited, a down feather was attracted as powerfully 

 yy the cork as by the tube itself. To convince 

 limself more completely, he procured a small ivory 

 >all, which he fixed at first to a stick of fir, four 

 nches long, which was thrust into the cork, and 

 found that it attracted and repelled the feather even 



