It was the English chemist Thomas Lane (1734-1807), who devised the instrument some time around 1766. In its most widespread version it consists of a Leyden jar in which the connecting rod with the internal plate terminates with a small conducting ball, at the height of which there is another conducting ball; the latter can be brought closer or taken farther away from the other by sliding its support along its guide, which is normally graduated and regulated by a micrometric screw.
The external plate is connected to the second ball and earthed; the internal one is connected to one of the plates of the battery of Leyden jars to be charged.
The other plate of the battery is connected to one of the poles of an electrostatic generator and finally the other pole of the generator is earthed. In this way the battery and the tube are connected in series and store up the same charge.
When the tension between the plates of the electrometric tube, thus the stored charge, reaches a certain critical point, a spark bridges the gap between the two spheres and the tube is discharged....continues