Mzzsos.—On the recent Sun-glows. 879 
would produce the effects with which we have been familiar. Such dust 
would cause a green reflection to be seen, followed by a yellow one. Then 
there would be competition between the red-arresting upper dust and the 
blue-dispersing lower air. Lower still the yellow would pass to orange, 
pink, and crimson—more striking as darkness increased. Perhaps there is 
„some analogy to this decomposition of white light and reflection of certain 
component rays, in the green colouring of the ocean, which Tyndall regards 
as resulting from the interruption of the usual green rays by impurities sus- 
pended in the water. If this matter be absent and the sea be deep as well 
as pure, it is of a blue colour. On Mount Whitney, Langley found the 
dust itself bright red, but the sky, as seen through it, violet; but near the 
sun quite white. He says red rays are transmitted with the greatest ease 
. through our air, the variation of colour depending on the size of the par- 
ticles of dust therein contained. Krakatoa may have charged the air, or a 
belt of it, with dust large enough to scatter the red rays and partly absorb 
the others. G. F. Chambers, at a January meeting of the Astronomical 
Society, mentioned the case of the crushing of seaweed by steam machinery 
at Eastbourne. The engineer of the works there says that he frequently 
sees the sun blue and green through the fine dust in the air. Dr. Buddle, in 
* Nature," on the 20th December, refers to the Frenchman in Algeria, who 
said one day when looking at the sun, C'est la premiere fois que j'ai vu le 
suleil bleu, and was informed that the dust from the Sahara was the cause 
of the novel colour. Ranyard's explanation is this: the particles of dust, 
when small compared with the wave-length of light or of invisible spectrum, 
disperse different proportions of red and blue—the larger the wave-length 
the less the intensity of dispersed light. Usually the colour of the sun is 
not affected by dust in the atmosphere. But when that dust is much in- 
creased in amount, the intensity of the dispersed light is much increased 
also, and the blue colour of the light between us and the sun affects the 
colour of the sun itself. Lockyer at first thought that the particles floating 
in the air were themselves blue and red, and thus that the colours we have 
witnessed were simply the result of reflection, and Hardwick’s ** Science 
Gossip " recently spoke of the blue and red partieles remaining. suspended 
in mid or upper air. But no such coloured particles have fallen, and so 
this hypothesis has been, I believe, generally abandoned. 
Ranyard in ** Knowledge " refers to the blue sun in the tropics becoming 
green as it neared the horizon, and sinking red. At Trincomalee, in 
Ceylon, from the 9th to the 12th September the sun rose green, and con- 
tinued to be of that colour till it reached the height of 10 degrees above the 
horizon, then it became blue, and at noon bright blue. During its declin- 
ing, similar changes were noted, but in the reverse order. The moon was 
