=+13.54 The accompanying summary quantities for x 5 particulate pollution (mg/m3

) and y 5 luminance (.01 cd/m2

)

were calculated from a representative sample of data that appeared in the article “Luminance and Polarization of the Sky Light at Seville (Spain) Measured in White Light” (Atmospheric Environment [1988]: 595–599).

a x 2 5 56,700 a y 2 5 8954 a xy 5 22,265 n 5 15 a x 5 860 a y 5 348