Jan. 3 1, 1S84 



KA TURE 



?09 



by means of the camera liicida, magnifying there 400 times, as 

 represented in Fig. 2. 



The crystals, as seen in Fig. 2 a, evidently exi^t in common 

 salt ; thi*: follows from their solubility in water, their crystalline 

 form, and their reaction in the flame. They are found in so 

 :jreat a number in the residuum of every drop of rain that we 

 oome to the conclusion that the^e little crystals must be found as 

 such in those regions of the atmosphere whe'e the dust is floating, 

 the air containing there hardly anything else but ice, and surely 

 little liquid water. 



In Fig. 2 1^ we see the crystals insoluble in water. They are 

 uncoloured and perfectly transparent, and may be considered 

 lo be the crj'stalline form of the ande itous mineral of which 

 the ashes consist for ihe greater part. 



The res'duum of the evaporated rain-drop of Januai-y 12 

 showed itself about in the manner seen in Fig. i. If the 

 window-pane is used as a slide and the du t examined 

 directly with the microscope, one will find there a great number 

 of little drops (bh. Fig. I), in mo^t of which a very fine sediment 

 i< seen of the constituents of the ashes ; in a fevv drops, however, 

 there are to be found crystaU of common salt {dd)\ further, 

 many loose crystals spread over the whole space [c<). Probably 



^V>^ 



>Fis.2. 



Fig. a (x 400). — Crystalline matter in the residue of- Fig. i. .4,cryit.ils 

 of common salt : B, crystals of the andesitous mineral, insoluble in «ater. 



the little drops are due to the presence of some hygroscopic 

 matter such as MgCU or CaCl, around some salt crystals. 

 I specially at the lower end of the whole drop assemble the 

 larger, glassy, black and brown particles of the ashes. 



The above prove? that during the last few vveeks crystals of a 

 ji.rrticular nature were floating in the air, and will perhaps ex- 

 plain the appearance of mock suns described by some of the 

 c' iservers of the after-glow. 



In a sample of original ashes from Krakatoa, when examined 

 in oil, I only found very few salt crystals, and the completely 

 outgrown andesit us crystals not at all. I am, however, con- 

 vinced that with I mger research I should have found the latter, 

 and others seem t > have discovered them indeed, but they are 

 without doubt veiy rare. So it seems to me that it m.ay be 

 taken for granted that in the atmospheric dust the proportionate 

 number of completely formed crystals is larger than in the 

 natural ashes, and the presence of so much common salt in the 

 upper air during these days is surely a remarkable fact. 



Wageningen, January 14 M. W. Beyerinck 



The atmospheric appearances frequently seen during the last 

 few months, principally at sunrise and sunset, from the similarity 

 of some of the manifestati jns to auroral appearance, have led 

 some persons to suspect cmneciion of the phenomena with 

 magnetism. 



Hitherto auroral exhibitions have, at Greenwich, been in- 

 variably accompanied by considerable magnetic disturbance, and 

 the absence of such disturbance on days on which the recent re- 

 markable atmospheric phenomena have been seen at Greenwich 

 seems conclu^ive as to the question of direct connection with 

 magnetisn. The Astronomer-Royal has therefore thought that 

 a brief statement of the circumstances in this respect might be 

 of interest to your readers. It appears that, either at sunrise or 

 sunset, unusual atmospheric appearances were seen at Greenwich 

 on November 8, 9, 13, 25, 26, 27, 28, 29, December i, 2, 4, 5, 

 6, 7, II, 17, and January 12 last. Of these day , on November 

 13 and January 12 the magnets were quiet, and on November 8, 

 9, 25, 26, 29, December 4, 5, 6, 7, and 17 very quiet; on 

 November 27, 28, December i, 2, and 11, there was a little 

 motion. The whole peri id was quiet generally as regards mag- 

 netic activity ; only at one time during the period from November 

 8 to January 12 was there any noteworthy disturbance, which oc- 

 curred on the days from November 19 to 22, and in no cise was 

 it in any degree remarkable. William Ellis 



Royal Observatory, Greenwich, January 26 



On p. 157 of your current volume you ask your "readers in 

 all parts of the world" to coainiunicate facts relative to the 

 singular sunsets which have been seen. 



Until seeing your request I had made no note of dates, but as 

 far as I can trust my memory the " after-glow " was noticed here 

 early in September, 18S3. On one night it lasted about two 

 hours after sunset. The phenomenon of " Contrast-Farben" 

 mentioned by von Helmholtz in Nature, December 6, 1S83, p. 

 130, I have noticed most markedly on two occasions — once in 

 October, and again on December 28 or 29, 1883. During this 

 year the sunsets on January 5, 9, 12, and 13, have been accom 

 panied by the "after-glow." 



About 12 o'clock on the I3'.h I saw a peculiar colour in the 

 neighbourhood of the sun, which on closer inspection was seen 

 to be in the form of an ellipse, the major axis being in the plane 

 of (he meridian. The length of this axis was about 50°. The 

 sun was situated nearer the upper extremity of this axis, in 

 breadth about 20°. The colour of this ellipse was a pale reddish- 

 violet ashen (if you can imagine such a combination). The sky 

 at the time was a deep blue, except in the ellipse. I suppose 

 the violet tinge was due to a combination of the red of what at 

 evening forms the " after-glow " and the blue sky. There were 

 a few clouds slowly moving from the west, and as one of these 

 approached the sun, when within about 6 diameters of the sun, 

 the edge nearer the sun becane coloured a faint yellow; then 

 followed (ale pink, dark pink, green, th-n again dark pink in 

 bands ; as the cloud floa'ed over the sun's disk one saw the 

 bands of co'our continuous, forming a halo. The clouds were 

 of a fleecy texture; I believe they were "cirro-stratus," not, 

 however, as open as what we call a "mackerel sky," and so 

 tenuous that they did not appreciably diminish the sun's bril- 

 liancy. The sunset on this day (January 13) was followed by a 

 mo.st intense "after-glow," but of only short duration. The 

 pink colour was at first in three broad rays, extending about 50° 

 from the point at which the sun disappeared, the central ray 

 almost vertical, one of the others on each side between the 

 central ray and the horizon. Afier a short time the intermediate 

 spaces became coloured red and then the colour ceased. 



The colour itself when most marked I can best describe as 

 that of burning cyanogen gas, a deep peach blossom. I have 

 noticed that the brilliant after-glows here have been preceded 

 by a dazzling glow, elhptical in shape, in the immediate neigh- 

 bourhood of the sun, tlie outer edge of this ellipse being com- 

 paratively dull and marked, and not having the same colour as 

 the sky a little further removed. The eastern horizon I have 

 also seen tinged pinkish before the colours make their appear- 

 ance in the west, and so marked has this been that I have 

 regarded it as a sign of the coming after-glow. 



I may add that for the last ten days the ground has been 

 covered with snow, and the temperature during the early part of 

 last week quite low, from 15°- 20° F. during the day. During 

 the end of the week the temperature was about 32° F. 



I have \\ ritten thus at length, hoping that there may be some- 

 thing of interest to you. Should you find anything it will give 

 me pleasure ; should you not, this will at least show you that 

 some of your distant readers would like to aid you in paths which 

 are not their own. W. G. Brown 



Univeisity of Virginia, U.S.A., January 15 



