Jan. 24, 1884] 



NATURE 



285 



or months would prob.ibly eject as much or more dust and ashes 

 than accompanied the Krakatoa co-vulsion, though not to so 

 great a heiijht. If, however, Mr. Preece's theory of electric 

 repulsion of the dust particles be true, then the finest of them, 

 if highly electrified, might rise to great heights, independent of 

 the force of ejectment from the volcano. 



In this connection it is well to remember that there njay have 

 been many other volcanic outbursts during the last few months, of 

 which we have not yet heard, and perhaps never may. The whole 

 chain of islands from Java to Alaska, including the Philippines 

 and Japan, is full of volcanoes, .and seems to be a fensitive seam 

 in the earth's crust. A convulsion like that of Krakatoa is 

 likely to be accompanied or followed by others along this line, 

 the northern portion of which is only visited by otter-hunters. 



Without presuming to question the theory as to the rapid 

 transmission of Krakatoa dust by the upper currents of the 

 atmosphere until we see the evidence on \\hich it rests, it oc- 

 curred to me that the above considerations might possibly 

 modify or supplement it in some degree. 



Referring tD the remarkable results deduced by General 

 Strachey, showing an atmospheric wave travelling three times 

 round the globe from the Krakatoa eruption, \\^hich seems to be 

 of even more scientific interest from a physical point of view 

 than the transmission of the dust and ashes, and which deserves 

 a thorough and careful re-examination when the data are in 

 fro'n all available barometric records, I would say that I have 

 been kindly alIo\\'ed ti examine the barometric records of the 

 Signal Office here at Washington, and I find no trace of any 

 such disturbance following the reported Alaskan eruptions of 

 October 6 and October 20. In connection with the record of 

 the waves following the Krakatoa catastrophe there are some 

 interesting points w hich I vvisli to examine more carefully before 

 discussing them. H. M Paul 



Washington, January 8 



Referring to Mr. Burder's letter in Nature of Janu.ary 10 

 (p. 251), is it so certain that, if there be no resisting medium in 

 interplanetary sp.ace, the whole of the earth's atmosphere mns( 

 "rotate with the earth as if it were part and parcel of it"? 

 Take a stratum of the atmosphere at, say, forty -five miles in alii, 

 tude at the equator. According to the received theory, this 

 ought of course to move with a velocity greater than that of the 

 surface of the earth immediately below. But each succ ssive 

 inferior stratum moves with less velocity. And thus they mu-t 

 tend to retard the superior strata with which they may be as- 

 sumed to be in contact. Of course the merging of stratum 

 into stratum is gradual, but this does not affect the amount of 

 friction and retardation. 



In like manner, imagine a section of the atmosphere taken 

 al ^ng the equator. Sections taken along successive parallels 

 of dtclination north and .south would tend to retard the veloc.ty 

 of this central layer. 



These t«o causes combined might have a considerable effect 

 in retarding the velocity of the upper atmosphere in equatorial 

 regions. And it seems to me doubtful whether the upper atmo- 

 sphere near the poles would be actually carried round with each 

 terrestrial rotation. The rarity of the upper regions of the 

 atmosphere and the lessened force of gravity \NOuId both help 

 towards the result indicated, inasmuch as they would tend to 

 make the atmosphere less rigid. 



As J am writing, I venture to make another sugge-tion. 

 Gilbert White mentions that in the summer of 1 783, when, as 

 at present, the atmosphere was filled with dast consequent on 

 volcanic eruptions, and " a peculiar haze or smoky fog prevailed 

 for many weeks in this island and in every part of Europe, and 

 even beyond its Hants," " all the time the heat was so intense that 

 butchers' meat could hardly be eaten the day after it was l.illed, 

 and the flies swarmed so in the lanes and hedges that they ren- 

 dered the horses half frantic, and ridmg irk.some." May not 

 the present May-like weather be due to a like cause? Sweet 

 violets, primroses, wallflowers, roses, and several other flowers 

 are now blooming in my garden under the Clevelmd Hills. 



Had the halos round the moon seen here last and the pre- 

 vious night any possible connection with the dust in the atmo- 

 sphere? I computed the diameter of the inner dirty white to 

 be twice, the dirty orange ov.e and three-quarters, and the outer 

 green three and a quarter times the moon's apparent diameter. 



John Haweli. 



Ingleby Greenhow Vicarage, Yorks, January 15 



I THINK a few notes relating to the recent sunsets may still 

 have an interest for some readers of Nature. Notwithstanding 

 the length of time these remarkable phenomena have been appa- 

 rent, the sunsets of January 1 1 and 12 were as brilliant as regards 

 the j(r(';/(/ after-glow as any that have preceded them, the final 

 glow having lasted on the 12th till 5.55 ; while the sun set that 

 evening at 4.12. 



The pink halo so often seen of late could not be discerned that 

 day though the sky was cloudless ; but it has been often visible 

 when clouds partly obscured the jun, or portions of the sky, and 

 could then be recognised between them, separating the blue of the 

 remoter sky from the whitish light surrounding the sun, as a ring- 

 formed glow of a strong pink colour. 



These broad pink balos have been less commented on than the 

 splendid sunsets which have invariably succeeded them, but they 

 have been nearly as persistent in their presence. You have had 

 so many accounts of the succession of colours and effects of the 

 two after-glows, that I will not allude further to them here ; but 

 as I have retained a record of many remarkable sunsets and sun- 

 rises which I observed in Wales in former days (possibly the very 

 same mentioned by Prof. Piazzi Smyth iu Nature, December 13, 

 18S3, p. 149, as observed by him thirty years ago), and as I care- 

 fully noted m them the time and hour of the changes in the sky 

 down to that of the complete extinction of the after light, it may 

 interest others than m.yself to compare displays of that date with 

 those of this winter. 



What is worthy of especial interest is the great difference 

 between the periods of prolongation then and now of the illu- 

 mination of the western sky, showing that the second after-glow 

 of recent sunsets is a phenomenon di-tinct from and additional 

 to those belonging to normal sunsets. 



The following table exhibits the two series of observations 

 made in 1855, 1S56, 1857, and in 1883-84 respectively : — 



The colours associated with the actual sunset are quite in 

 accord in both. 



The first after-glow, or pink cone or dome of light appearing 

 after the sunset colours have nearly faded, is also similar in both 

 series, but its time of setting has been apparently somewhat 

 prolonged in the recent observations. 



It is the 1SS3-84 series alone, however, that shows \)xt second 

 after-glow, and the duration of this strange phenomenon, which 

 I have the advantage of observing over a wide bird's-eye view in 

 Norili Wilishire, has extended on evenings when it could bewell 



