Meeson. — On the recent Sun-ylows. 379 



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 tbe 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 brigbt 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. Gr. 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. Buddie, in 

 " Nature," on the 20th December, refers to the Frenchman in Algeria, who 

 said one day when looking at the sun, West la premiere fids que fai vu le 

 suleil bleu, and was informed that the dust from the Sahara was the cause 

 of the novel colour. Eanyard'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 Hard wick's " Science 

 Gossip" recently spoke of the blue and red particles remaining suspended 

 in mid or upper air. But no such coloured particles have fallen, and so 

 this hypothesis has been, I believe, generally abandoned. 



Banyard 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, aud at noon bright blue. During its declin- 

 ing, similar changes were noted, but in the reverse order. The moon was 



