A Lippmann electrometer is a device for detecting small rushes of electric current

Electric current

Electric current is a flow of electric charge through a medium.This charge is typically carried by moving electrons in a conductor such as wire...

 and was invented by Gabriel Lippmann

Gabriel Lippmann

Jonas Ferdinand Gabriel Lippmann was a Franco-Luxembourgish physicist and inventor, and Nobel laureate in physics for his method of reproducing colours photographically based on the phenomenon of interference....

. The device consists of a tube which is thick on one end and very thin on the other. The thin end is designed to act as a capillary

Capillary action

Capillary action, or capilarity, is the ability of a liquid to flow against gravity where liquid spontanously rise in a narrow space such as between the hair of a paint-brush, in a thin tube, or in porous material such as paper or in some non-porous material such as liquified carbon fiber, or in a...

 tube. The tube is half-filled with mercury

Mercury (element)

Mercury is a chemical element with the symbol Hg and atomic number 80. It is also known as quicksilver or hydrargyrum...

 with a small amount of dilute sulfuric acid

Sulfuric acid

Sulfuric acid is a strong mineral acid with the molecular formula . Its historical name is oil of vitriol. Pure sulfuric acid is a highly corrosive, colorless, viscous liquid. The salts of sulfuric acid are called sulfates...

 above the mercury in the capillary tube. Metal wires are connected at the thick end into the mercury and at the thin end into the sulfuric acid.

When the pulse of electricity arrives it changes the surface tension

Surface tension

Surface tension is a property of the surface of a liquid that allows it to resist an external force. It is revealed, for example, in floating of some objects on the surface of water, even though they are denser than water, and in the ability of some insects to run on the water surface...

 of the mercury and allows it to leap up a short distance in the capillary tube. This device was used in the first practical ECG machine which was invented by Augustus Desiré Waller

Augustus Desiré Waller

Augustus Desiré Waller FRS was a British physiologist and the son of Augustus Volney Waller. He was born in Paris, France.He created the first practical ECG machine with surface electrodes.He died in London.-Further reading:...

.