Sentence:  How does it work, though? It's based on the observation made some 200 years ago that <WSD>electricity</WSD> can change the shape of flames. 
Meaning of the word marked with <WSD> tags:  Originally, a property of amber and certain other nonconducting substances to attract lightweight material when rubbed, or the cause of this property; now understood to be a phenomenon caused by the distribution and movement of charged subatomic particles and their interaction with the electromagnetic field. (from 17th c.)