Measurement of the Electric Current in a Kpc-Scale Jet

We present radio emission, polarization, and Faraday rotation maps of the radio jet of the galaxy 3C303. From this data we derive the magnetoplasma and electrodynamic parameters of this 50 kpc long jet. For a {$\sim 2$} kpc segment of this jet we obtain for the first time a direct determination of a {\it galactic}-scale electric current ($\sim 3 \times 10^{18}$A),anditsdirection$-$ {\it positive} away from the AGN. Our analysis strongly supports a model where the jet energy flow is mainly electromagnetic.