The Leyden Jar was the earliest manifestation of a high-voltage capacitor.
Batteries of Leyden Jars enabled early electrical experimenters to store the high-voltage output of their frictional machines. Large amounts of energy could be accumulated, the effects of the subsequent violent discharges being of great interest. Nollet, for instance, simultaneously electrocuted the whole community of a convent.
Leyden Jars from "Rudimentary Electricity" by Snow-Harris 1853.
Leyden Batteries from the same.
As is usual for "The Young Man's Book of Amusement", the Leyden Jar Experiments encourage highly ill-advised activities, such as "...and a discharge of six square feet will deprive a man of sensation for a time, if the head be made part of the circuit."