The **logarithmic** formulae for these concentration cells indicate that theoretically their electromotive force can be increased to any extent by diminishing without limit the concentration of the more dilute solution, log c i /c 2 then becoming very great.

The results give equations of the same **logarithmic** form as those obtained in a somewhat different manner in the theory of concentration cells described above, and have been verified by experiment.

On the analogy between this case and that of the interface between two solutions, Nernst has arrived at similar **logarithmic** expressions for the difference of potential, which becomes proportional to log (P 1 /P 2) where P2 is taken to mean the osmotic pressure of the cations in the solution, and P i the osmotic pressure of the cations in the substance of the metal itself.

A volume entitled Opera posthuma (Leiden, 1703) contained his "Dioptrica," in which the ratio between the respective focal lengths of object-glass and eye-glass is given as the measure of magnifying power, together with the shorter essays De vitris figurandis, De corona et parheliis, &c. An early tract De ratiociniis tin ludo aleae, printed in 16J7 with Schooten's Exercitationes mathematicae, is notable as one of the first formal treatises on the theory of probabilities; nor should his investigations of the properties of the cissoid, **logarithmic** and catenary curves be left unnoticed.

When, by practice with logarithms, we become familiar with the correspondence between additions of length on the **logarithmic** scale (on a slide-rule) and multiplication of numbers in the natural scale (including fractional numbers), A /5 acquires a definite meaning as the number corresponding to the extremity of a length x, on the **logarithmic** scale, such that 5 corresponds to the extremity of 2X.