A measurement of the derivative (delta ln F-2/delta ln x)(Q2) equivalent to
-lambda (x, Q(2)) of the proton structure function F-2 is presented in the
low x domain of deeply inelastic positron-proton scattering. For 5 x 10(-5
) less than or equal to x less than or equal to 0.01 and Q(2) greater than
or equal to 1.5 GeV2, lambda (x, Q(2)) is found to be independent of x and
to increase linearly with ln Q(2). (C) 2001 Elsevier Science B.V. All right
s reserved.