This is a reed electrometer that derives from the quadrant electrometer; but there are only two quadrants and the needle is also substantially halved and has the characteristic form of a reed.
The reed is made of aluminium, its mass is just one milligram, it is attached to a very thin platinum wire (Wollaston wire) stretched vertically and elastically at both ends, and is balanced, on the side opposite the wire, by a miniscule counterweight. In this way, the barycentre of the reed-counterweight system falls on the wire and the device is almost completely independent of gravity and is quite resistant to bumps.
During transportation, the reed of the instrument does not need to be blocked and prior to use it need not be levelled; it also supplies a prompt response and is quite stable.
The working is like that of the quadrant electrometer and the possible connections are also the same.
By means of a micrometric screw with precision to a hundredth of a millimetre, the two quadrants can be brought closer to or taken farther away from the reed, thus increasing or decreasing the sensitivity of the instrument...continues