The auroral electron data obtained during the flight of Polar 3 over an auroral arc (Maynard et al., 1977) were utilized as an input to a computation of the Hall and Pedersen conductivities of the auroral ionosphere produced by the particle precipitation. These conductivities, together with the in situ electric field measurements made on board the rocket, allowed an analysis of the electrodynamics of this auroral arc to be carried out. It was found that the local electric field variations correlated very well with the reciprocal of the height-integrated Pedersen conductivity, a result suggesting that the auroral ionosphere was, to an extent electrically isolated from the source of the electric field in the outer magnetosphere. The Joule power dissipation associated with ionospheric current flow was found to decrease abruptly from a value of ~12 ergs/cm2/s column equatorward the arc to a very low value within the confines of the arc. However, the sum of the Joule dissipation and the electron energy flux, which is the total energy input to the neutral atmosphere, did not display any abrupt variation across the equatorward boundary of the acr. The auroral electrojet, inferred from J=&sgr;⋅E by assuming no neutral winds, was not directed parallel to this arc, nor was the current intensified within this arc. Instead, the electrojet flowed in a sheet extending equatorward from this arc for a distance of at least 100 km. The presence of an E region neutral wind will greatly affect the current patterns within this arc but will have only a first-order effect on the current system equatorward of this arc. These observations are generally consistent with a model of auroral arc in which resistivity along the magnetic field lines linking the auroral ionosphere to the outer magnetosphere isolates these two regions from one another and results in magnetic-field-aligned potential differences which may accelerate auroral electrons.