A Sunset Phenomenon on July 22

Abstract

REFERRING to the sunset phenomenon seen on July 22, and described in NATURE of July 27, it seems probable from information kindly sent by various correspondents that the clouds seen were somewhere in the neighbourhood of Plinlimmon. If this were the case, the height of the tops of the clouds would have been from 18,000 to 18,500 ft., and the two clouds would have been about eight miles apart. A correspondent who watched the sunset from Minchinhampton Common reports that no clouds were visible from there, but even from so far west the altitude of clouds at a height of 18,000 ft. over Plinlimmon would not have exceeded 1° 40′, and they would have only been visible if the horizon were a good one and the atmosphere very clear. In asking for information from Ireland I was casting my line too far; the top of a cloud the height of which is 24,000 ft. (which is probably high for a cumulo-nimbus in these latitudes) would not be visible more than 190 miles away. The distance of Plinlimmon from Farnborough is 154 miles; clouds at such distances can probably only be seen when the sun sets behind them in an otherwise clear sky.