Martian relief and the coming opposition

In the report "Martian relief and the coming opposition" (3 Mar., p. 1100), D. H. Harris stated that, "... the reduced contrast with decreasing (terminator distance) just balances the increase in visibility due to shadow length." This is obviously erroneous. A more careful examination of the problem shows that for favorable values of the Aerocentric EarthSun Sun angle, visibility of relief increases toward the terminator, clouds not withstanding.