In the two hundred years that followed William Gilbert's De Magnetica, the word "electric" came to be applied not only to amber, but to any material that generated static electricity when rubbed.
Charles François de Cisternay du Fay (1698-1739) studied the range of these "electrics" and posited the existence of two forms of electricity: vitreous (generated from glass) and resinous (generated from resins / amber). He used the expression "non-electric" to refer to conductive materials (metals). "Electrics" did not, in du Fay's view conduct electricity...
Therefore, the discovery of the Leyden Jar threw the scientific community into a tizzy, because glass was supposed to be an insulator. The phenomenon would remain an enigma for some time.
Benjamin Franklin's theory that electricity was a single phenomenon that appeared in either positive or negative states, displaced du Fay's vitreous-resinous theory, but while Franklin posited that the glass held the charge, he didn't really explain how or why. Franklin's theory's were a sufficient black box, enabling electrical science to move forward...
Several decades later, Michael Faraday needed terminology that didn't carry the baggage associated with "electric" and "non-electric." His friend William Whewell suggested "dielectric" ...
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