ライデン瓶
Starting in late 1756, Franz Aepinus, in a complicated interaction of cooperation and independent work with Johan Wilcke, developed an "air condenser", a variation on the Leyden jar, by using air rather than glass as the dielectric. This functioning apparatus, without glass, created a problem for Benjamin Franklin's explanation of the Leyden jar, which maintained that the charge was located in the glass.