Contributions to a theory of the capillary electrometer. -I. —On the insulation resistance of the capillary electrometer, and the minimum quantity of electricity required to produce a visible excursion

What may be called the Insulation Resistance of the capillary electrometer is important for two reasons—first, as to its bearing on the theory of the instrument, and secondly, as affecting the method of using it in dealing with electrical charges or quantities of limited amount. I propose briefly to record some of my own experiments on, this head. In many capillary electrometers, if an excursion of the meniscus is produced by touching the terminals with a source of electromotive force and then removing it, leaving the circuit open, the meniscus returns in a comparatively short time to the position it would occupy if the instrument were short circuited. In other words, the charge, which, as Lippmann showed, is contained in the instrument as long as the meniscus is deflected from its zero position, gradually leaks away.