It is now required to bring this definition experimentally into action, i.e., to realize an interval of time which may be a known multiple of [rho].  This problem may be solved in various ways,[1] and especially by means of the following apparatus.

   [Footnote 1:  In this system the measurement of time is not
    effected, as ordinarily, by observing the movements of a
    material system, but by experiments of equilibrium.  All the
    parts of the apparatus remain immovable, the electricity alone
    being in motion.  Such appliances are in a manner clepsydrae.  This
    analogy with the clepsydrae will be perceived if we consider the
    form of the following experiment:  Two immovable metallic plates
    constitute the armatures of a charged condenser, and attract
    each other with a force, F. If the plates are insulated, these
    charges remain constant, as well as the force, F. If, on the
    contrary, we connect the armatures of resistance, R, their
    charges diminish and the force, F, becomes a function of the
    time, t; the time, t, inversely becomes a function of P. We
    find t by the following formula: 

        t = [rho] x (lS / S[pi]es) x log hyp(F0/F)

F0 and F being the values of the force at the beginning and at the end of the time, t.  The above formula is independent of the choice of units.  If we wish t to be expressed in seconds, we must give [rho] the corresponding value ([rho] = 1.058 X 10^-16).  If we take [rho] as a unit we make [rho] = 1, and we find the absolute value of the time by the expression: 

        (lS) / (8[pi]es) log hyp(F0/F)

We remark that this expression of time contains only abstract numbers, being independent of the choice of the units of length and force.  S and e denote surface and the thickness of the condenser; s and l the section and the length of a column of mercury of the resistance, R. This form of apparatus enables us practically to measure the notable values of t only if the value of the resistance, R, is enormous, the arrangement described in the text has not the same inconvenience.]

A battery of an arbitrary electromotive force, E, actuates at the same time the two antagonistic circuits of a differential galvanometer.  In the first circuit, which has a resistance, R, the battery sends a continuous current of the intensity, I; in the second circuit the battery sends a discontinuous series of discharges, obtained by charging periodically by means of the battery a condenser of the capacity, C, which is then discharged through this second circuit.  The needle of the galvanometer remains in equilibrium if the two currents yield equal quantities of electricity during one and the same time, [tau].