The ordinary Lippmann type of capillary electrometer consists of a single fine tube in which the rise of mercury depends upon the impressed voltage for small voltages up to one volt. The new capillary electrometer here discussed is an inverted U tube device whereby direct readings of the pressure difference between the two mercury levels can be made, thus obviating the necessity for assuming that the large surface in the reservoir is unchanged. Its advantages lie in its comparative simplicity, its sensitivity (one volt corresponding to 1.5 cm deflection compared with .5 cm for an ordinary Lippmann type instrument), and its direct readings. The instrument is a result of an investigation into the laws of capillary electrometric phenomena. Lippmann's voltage-height relation is verified in an independent manner and extended to tubes of different radii. A new relationship is found and extended to tubes of different radii. A new relationship is found, that between the rise of the mercury and the radius of the tube. A simple curve represents this result, but a simple analytic expression does not exist due to the extreme complexity of the phenomenon as theory shows.
CLARENCE E. BENNETT, "A NEW CAPILLARY ELECTROMETER, AND THE RELATION BETWEEN THE MERCURY DISPLACEMENTS AND THE RADIUS OF THE TUBE," J. Opt. Soc. Am. 11, 411-412 (1925)