[en] The ratio of the proton's elastic electromagnetic form factors, G_Ep/G_Mp was obtained by measuring P_t and P(ell), the transverse and the longitudinal recoil proton polarization, respectively. For elastic ep → ep, G_Ep/G_Mp is proportional to P_t/P(ell). Simultaneous measurement of P_t and P(ell) in a polarimeter provides good control of the systematic uncertainty. The results for the ratio G_Ep/G_Mp show a systematic decrease as Q² increases from 0.5 to 3.5 GeV², indicating for the first time a definite difference in the spatial distribution of charge and magnetization currents in the proton