Lippmann electrometer

[1] 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 tube.

When the pulse of electricity arrives it changes the surface tension 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.

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