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Published online by Cambridge University Press: 08 February 2017
An upper limit to the amplitude of the overall density fluctuation has been found by means of the gravitational lensing effect of the density inhomogeneity on luminosity of quasars with large redshifts. The observed differences of luminosities of quasars located at different directions are partially given by the lensing effect; therefore, a useful upper limit to the inhomogeneity can be derived.