ofspecimenpreparation,andgreaterversatilityinvaryingthemechanismsfor achievingimagecontrast.Digitalimageanalysishasexpeditedparticlesize analysisfrommicrographs(SaxandOttino,1073;Nishietal.,1988;Kruse, 1973;VeselyandFinch,1988)atresolutionlimitsofafewAngstroms