ELECTRICAL PROPERTIES OF SILK. 159 



ittached by very fine brass and iron wire, but, to 

 ;heir utter astonishment, found the effect exactly 

 ,he same as when they used the hempen cord ; the 

 electrical virtue utterly passed away ; while, on the 

 >ther hand, when the packthread was supported by 

 i silken cord, they were able to convey the electric 

 virtue seven hundred and sixty-five feet. 



It was evident, therefore, that these effects cle- 

 >ended upon some peculiar quality in the silk, 

 yhich disabled it from conducting away the elec- 

 trical power, as the hempen cord and the wire had 

 done. 



The accidental discovery of Mr Gray led to 

 the knowledge of the non-conducting powers of 

 various other substances; and since the nature 

 )f electricity has. been more deeply investigated, 

 the true electric properties of most substances have 

 >ecome known, and are now divided into elec- 

 trics and non-electrics. The following substances 

 are among the principal conductors of the electric 

 fluid ; namely, stony substances in general, more 

 especially those of a calcareous nature, such as lime, 

 marble, &c., sulphuric acid, black pyrites, black 

 ead, alum, charcoal, all the metallic ores, the ani- 

 mal fluids, and all other fluids excepting air and 

 oils. 



The electric bodies are those substances which, 

 when excited, collect or omit this fluid, such as 

 amber, sulphur, jet, glass, and all precious crystal- 



