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The Voyager 2 photopolarimeter was reprogrammed prior to the August 1981 Saturn encounter to perform orthogonal-polarization, two-color measurements on Saturn, Titan, and the rings. Saturn's atmosphere has ultraviolet limb brightening in the mid-latitudes and pronounced polar darkening north of 65 degrees N. Titan's opaque atmosphere shows strong positive polarization at all phase angles (2.7 degrees to 154 degrees ), and no single-size spherical particle model appears to fit the data. A single radial stellar occultation of the darkened, shadowed rings indicated a ring thickness of less than 200 meters at several locations and clear evidence for density waves caused by satellite resonances. Multiple, very narrow strands of material were found in the Encke division and within the brightest single strand of the F ring.

Four groups of 20 subjects each made magnitude judgements of either length or numcrousness either with a designated modulus or with freedom to select their own modulus. After a logarithmic transformation of the data from each subject, a residual measure was computed as ihe deviation of a response to a stimulus from the average of all responses to that stimulus. The residuals on successive presentations were found to correlate positively. They were also found to be related to their serial position within the presentation sequence. The results indicate a tendency for subjects to change the unit of their numerical estimates during the judgement sequence. Implications of sequential response effects for estimates of the exponent of the psychophysical power function were discussed. KKSUMK Quatrc groupes de 20 sujcts chacun faisaicnt des jugements dc longueur ou dc nombre soil avec un module designc ou avec la libcrtc de seleclionncr leur propre module. Aupres une transformation logurithmique des donnees pour chaque sujet, unc mesure residucllc ctait calculee comme la deviation dc la reponse a un stimulus par rapport la moyenne de toutcs Ics rcponses a cc stimulus. Les residuelles sur des presentations successives corrclaienl positivement. Elles etaient aussi reliees a leur position serielle dans la sequence de presentation. Les resultats indiquent unc tendance pour les sujcts a changer ('unite dc leurs eslime's numcriques pendant la sequence de jugement. Les implications des effeis de reponse sequentiellc pour des estimes de l'cxposanl de la puissance de la fonction psychophysique sont discutees.

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