XXL.—Observations on the Polarisation of the Atmosphere, made at St Andrews in 1841, 1842, 1843, 1844, and 1845

Abstract

During the last half century, observations on the polarisation of the atmosphere were made by several eminent observers—by Arago, Delezenne, Babinet, and Zantedeschi; but no result of special importance was obtained till Arago made the great discovery that there existed in the atmosphere a point, or spot, in which there is no polarisation. At sunrise or sunset he found that this neutral point was 20° or 30° above the point opposite to the sun, or what we may call the Antisolar point. The name of Arago's neutral point has been given to this spot without polarisation. It is best seen after sunset. At St Andrews it is above the horizon all the day, between the middle of November and the end of January.