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During the past year the subject of power transmission by multiple-conductor circuits has received considerable attention. The formulas and estimating curves given in the paper may therefore be of interest at this time. Formulas are developed for the inductance and capacitance to neutral per phase and the approximate corona starting voltage of perfectly transposed, multiple-conductor, three-phase transmission lines having any number of conductors per phase. For certain special arrangements of the conductors, curves are given for the 60-cycle reactance, capacity susceptance, and corona starting voltage. These curves show the effect of variations, throughout their practical range, in conductor diameter, spacing between phases and between conductors of the same phase. Two, three, four and five conductors per phase are considered. A comparison is made of multiple- and single-conductor circuits with respect to charging current, voltage at no load, power which can be carried with the same voltage drop, and stability.