Dec. U, 1883.] 



♦ KNOWLEDGE ♦ 



365 



particles of iron, easily separable by a magnet from the organic 

 dust (of which, by-the-bye, there is very little) accompanying 

 it. The wonderful crimson of the sky here on the nights 

 of the 4th and 5th were accompanied by the beautiful 

 spectacle of a Green Moon. My own idea was that this was 

 simply a retinal effect of contrast ; but that very accurate and 

 painst.iking observer, Mr. H. Pratt, P.R.A.S., of Brighton, seems to 

 have examined the moon with a two-inch achromatic telescope, so 

 as to cut off all the light of the sky, with the result that he " found 

 the bluish-green tint of the moon more decided and beautiful than 

 before." This would seem to point to the dichroisra of the 

 reflecting medium — whatever it may be — to which we are indebted 

 for the recent gorgeous phenomena. I may add that my butler tells 

 me that this morning's sunrise was similar to some of the recent 

 abnormal ones ; but I did not see it myself. 



Forest Lodge, Maresfield, Uckfield, Willi.\m Noble. 



Dec. 10, 1883. 



LUNAR SHADOWS.— STRANGE SUNRISE AND SUNSET 

 EFFECTS IN LANCASHIRE. 



[1041] — I read with interest the Rev. J. W. Webb's article in 

 Knowledge, of Nov. 16th, on " Lunar Delineation " ; but he seems 

 to me wrong in saying that the " shadows are of unbroken black- 

 ness," owing to the want of a "reflective atmosphere," and that 

 the facility of delineation would therefore be increased ! If 

 such were the case, a moon-picture would indeed be a simple affair 

 — nothing but fields of light surrounded by utter blackness. Now, 

 one reason a moon-pietnre wonld be worth doing is that, although 

 the sky or space behind the monntains would be absolutely black, 

 there is no reason why the shadows in the monntains should be so ; 

 on the contrary, they might be full of bright reflections from the 

 intense glare on the exposed parts of rock, and — as the Rev. J. W. 

 Webb well knows — a moment might be chosen when only the 

 highest peaks catch the sun's light, so that the rest of the rocks 

 and foreground might be without any sharp shadows at all. I 

 don't understand why he uses the words " reflective atmosphere." 

 Isn't it enough to say that the moon is ivithout atmosphere ? 



At Coniston we have had wonderful effects over the lake. I 

 have been in the habit of watching the sky all my life, being a sea 

 and sky painter, but have never seen such extraordinary effects. 

 One morning, Coniston Old Man (2,600 feet), was quite red, and 

 this before sunrise, when it was almost dark. It never lost its 

 light, but there were no shadows until nine o'clock, when, I suppose, 

 the sun's real light began to reach it. The other evening at a 

 quarter to five, we had cast shadows from the intense glare of 

 illuminated vaponr above the sunset, and the crescent moon to the 

 left looking pale blue. Arthur Severn. 



[I have ventured to add to Mr. Severn's letter on Lunar 

 Delineation, a portion of the letter accompanying it, which (as a 

 whole) was not intended for publication. — R. P.] 



THE ERUPTION IN THE SUNDA STRAITS. 



[1042] — Ceylon has been more or less affected by the volcanic 

 eruption in the Straits of Sunda. Ponang also, which is 800 miles 

 off, heard the noise plainly. We are 1,600 miles. I heard the 

 noise as of distant artillery. We had in Colombo, at Guler, and at 

 Point Pedro — west, south, and north of our island — a tidal-wave 

 first to recede, then to advance. At Cape Comorin, soutii point of 

 India, this extended to half a mile. We presume the agitation of 

 submarine forces was extensive, and had for its centre an island in 

 the Straits of Sunda, which had been silent for 200 years. 



A concurrent phenomenon has been the aspect of the sun before 

 setting. Ho has, from olive green, become pale sea-green, and anon 

 the a])I^earanoe of a pale full moon, so that the largo spot at the 

 left, rather above midway, could be seen without difliculty, as we 

 could gazo at him without the necessity for coloured glass. 



The interesting point is whether this green is from the sun's 

 gases, or whether from atmospheric causes around this portion of 

 the earth. I should bo glad to know' whether during the past week — 

 say back from Sept. 11 inclusive — tho sun bore the green aspect in 

 England. Certainly 1 never saw the sun green before. The weather 

 of late has been abnormal — very dense, white, and leadou-eoloured 

 clouds. 



If tho sun was not green elsewhere — in England, for instance — 

 then we must conclude it is from purely local atmospheric causes 

 liereabouts. If he has looked green at home and elsewhere, then 

 tho (|ue8tion reduces itself to whether it has been caused by the 

 earth's unusual atmosphere or from tho solar disturbance. 



Colombo, Ceylon, Sept. 13, 1883. H. L. 



GREAT SEA-WAVE. 



[1043]— On Aug. 27 the inhabitants of the seashore were thrown 

 into consternation by seeing at about 1.30 the sea suddenly recede, 

 leaving in some places reefs and foreshore dry, and then as suddenly 

 rising to an unusual height half-an-hour afterwards. This continued 

 at intervals all the afternoon, casting boats adrift, stranding them 

 and a lot of fish which were caught napping, and were then promptly- 

 picked np by the aborigines. Beyond this no mischief was done 

 here. Most people attributed it to volcanic action (for we are not 

 altogether strangers to these matters,'and, indeed, keep an active 

 volcano of our own at Bourbon), and a good many people felt a 

 slight shock. I did not. Probably the shocks would have been 

 more generally felt had they occurred in the evening, or at a time 

 when most people are quiet. Wo had, however, no idea at the 

 time that the origin of what we saw was so distant, and that we 

 were feeling only the contre-conp of the fearful catastrophe of 

 the Sunda Straits. Little by little, news has been received from 

 every part of the Indian Ocean, and it would appear that even as 

 far as the African coast the wave extended. At Tamatave, a 

 friend of mine was sitting with several people on the beach, when, 

 to their amazement, they saw the sea recede so much that the 

 French men-of-war which had just bombarded the place were all but 

 stranded. This was at 3.30. With us the first wave was at_1.30._ 



It would seem that there is a renewal of volcanic activity in 

 many parts of the world ; and of late the light of Bourbon volcano 

 has at times been seen from here at night. 



I can hardly see how the tilings are related, but it is certain that 

 about that time we were favoured with a series of the most 

 extraordinary sunsets and sunrises that I ever ivitnessed, even here, 

 where we are famous for them. Our Astronomer Royal gives a 

 lame sort of explanation about the passage of light through volcanic 

 dust, but none of that has been seen here. At Seychelles the same 

 phenomena ars reported, and there the sun rose in the wrong place 

 one fine morning, and did not get right again tUl some time late in 

 the morning. ['This must refer to abnormal sunlight, not to sun's 

 disc— R. P.] 



If our sunsets had happened in the hurricane season we should 

 have known what to expect, which wonld have been what the 

 sailors call "beans" (refer to Mr. M.), but in August and Sep- 

 tember there is no excuse for them. 



One sunset in particular I remember. If Turner had painted it, 

 it would have been said that on that day he was either delirious or 

 drunk. I was coming into town one evening by train, at about 

 5.30 to 5.45 (you are for ten minutes or so in view of the setting 

 sun and a wide stretch of ocean). Tliat evening the sea was a bath 

 of mercury, or molten lead, streaked with black. The sun, but a 

 few degrees above the horizon, was a yellow, blurred opening in the 

 haze ; the sky was one mass of streamers of every colour, and what 

 ought to have been blue was leaf -green ; the air was orange-colour, 

 and everything was as though seen through a glass of that colour. 

 Tliis strange sight terminated by a performance which is rare in 

 ordinary times, but has frequently appeared of late. Tho sun sets, 

 and it seems as though night were coming on more rapidly than 

 usual, when, behold! the whole concern lights np again, and it 

 becomes lighter than before. The sun sets, but the light is 

 ghastly and ill-conditioned ; ten minutes afterwards all is dark. In 

 the morning tho reverse ha])pens. Long before sunrise, the sickly 

 yellow light suddenly glares upon us, making the sky as a grass- 

 plot, and all things "hideous; this lasts fifteen minutes, and com- 

 parative darkness sets in ; then the sun rises as it should. What 

 connection has this with volcanoes ? Querj-. Can you answer ? 



Port Louis, Mauritius. A Correspondent. 



MOON'S MOTIONS. 



[104-1] — The nearer any body is to the stm, the more light it will 

 receive, therefore the brighter it will shine, and will appear brighter 

 to an observer on a neighbouring body. 



(1.) During a complete revolution of the moon, with respect to 

 the earth, she will vary her distance from the sun about half a 

 million miles. (2.) By the earth's revolution round the sun, the 

 moon is iu winter brought three million miles nearer at that time 

 than in summer. So that, viewing tho full moon in December, 

 should it not bo brighter and larger than the full moon in June, 

 seeing that it is three million miles nearer to the source of light ? 



Being a science teacher, I have lately been giving lessons on tho 

 " Moon," and have endeavoured to explain the longer moonlight of 

 winter than of summer, greater height in heavens, Ac, and was 

 struck with the idea mentioned above. I have not seen it mentioned 

 in any text-book I possess. 



Another matter 1 should like to ask your opinion about, and that 

 is — '■ We may get an idea of its (the moon's) motion round the 

 Bun, it we imagine a wheel going along a road to have a pencil fixed 



