Abstract: | We report on a measurement of the proton structure function F 2 in the range 3.5 × 10?5 ≤ x ≤ 4 × 10?3 and 1.5 GeV2 ≤ Q 2 ≤ 15 GeV2 at the ep collider HERA operating at a centre-of-mass energy of ${sqrt s} = 300 {? GeV}$. The rise of F 2 with decreasing x observed in the previous HERA measurements persists in this lower x and Q 2 range. The Q 2 evolution of F 2, even at the lowest Q 2 and x measured, is consistent with perturbative QCD. |