"[W]hen a white object is seen in the open air... shadows are blue... in accordance with the fourth proposition—'the surface of every opaque body partakes of the colour of surrounding objects.' ...that part which is not exposed to the sun remains in shadow, and only partakes of the colour of the atmosphere. And if this white object should neither reflect the green of the fields which stretch out to the horizon nor... face the brightness of the horizon itself, it would undoubtedly appear of such simple colour as the atmosphere showed itself to be."