Art. XLIX.—Red Sunsets.
[Read before the Philosophical Institute of Canterbury, 1st May, 1884.]
The equatorial diameter of the earth is 7,901 miles, and the circumference is 24,825 miles, and, as she revolves once on her axis in 24 hours, a place on the equator moves through 1,034 miles per hour, but at any depth
beneath the surface the velocity is less in proportion to that depth; in like manner, if we look on the atmosphere as part and parcel of the earth, at a certain height the velocity is greater in proportion to the height.
The whole world has been greatly interested during the last seven or eight months by the beautiful phenomena of coloured suns and brilliant sunsets, and the liveliest interest has been exhibited as to their origin. Lockyer was the first, I believe, to point out the fact of the phenomenon of coloured suns appearing first in the east and then gradually shifting to the west. He traces them to Panama, and then speaks of them as having been seen on a north and south line; but it strikes me that after leaving Panama the phenomenon passed still further westward, seen on the 3rd September 4,000 miles west of Panama, and at Honolulu on the 5th, and struck India and Ceylon on the 8th September, thus performing more than a complete circuit of the globe; moreover, I am of opinion that it may be traced still further westward, where it was seen in lat. 24° 06′ N., long. 140° 29′ W., by Captain Penhallow of the barque “Hope,” on the 25th September, having then performed 2 ¾ revolutions of the globe.
All the information that I have collected, and from which I have compiled the following tables, has been obtained from “Nature.” The time column has been deduced from the time and date of the phenomena appearing at the different stations, reduced to Krakatoa time. In some instances great difficulty has been experienced, especially in reference to the time at Maranham in Brazil, and at Trinidad, and it has been concluded that at those two stations the times are late, because it was seen at Panama before the time given at them, which we suppose to be an error. Likewise in the case of the Gold Coast, in one place the date given is the 30th August, and in another the 1st September, but from the general result it would appear that it reached that locality about midnight 30th—31st August.
The tables, I trust, are sufficiently clear. The first column of miles represents the mean diurnal velocity that the cloud travelled at between Krakatoa and the different localities en route; and in the subsequent columns are given the same from each station in rotation. Of course it will be understood that a small error of an hour or two in the time at the stations comparatively close to the eruption would make a large difference were we to show the diurnal velocity: and as I have had only a week' notice to prepare this paper, I trust that any errors that may be hereafter found will be treated with that consideration.
Table I., showing the Mean Diurnal Velocity, in English Miles, of the Phonemena of Coloured Suns and Brilliant Sunsets, in the Northern Hemisphere:—
[The section below cannot be correctly rendered as it contains complex formatting. See the image of the page for a more accurate rendering.]
|—||Time from Java to||Java.||Seychelles.||East Coast of Africa.||Gold Coast.||Maranham.||Trinidad.||Panama.||4000 miles W. of Panama.||Honolulu.||India.|
|E. Coast of Africa||53 D.||1817||1873|
|4000 miles West of Panama||8¼||2061||2424||2210||2493||2370||2338||2000|
|Lat. 24° N. Long. 140 30 W.||29⅔||2132||2246||2206||2268||2165||2400||2170||2460||2316||2192|
Arithmetical mean = 2105 miles per diem.
True mean of 1st column = 2095 "
The true mean of the first column, viz., that under the head of Java, is obtained by adding the distance between Krakatoa and each separate station together, and dividing the aggregate by the gross total number of days. The way by which the distance between any two stations is derived is by multiplying the difference in degrees of longitude by the value of a degree in English miles, for the mean latitude of the two places. It must be remembered that between India and the last-named locality on the list, the dust cloud is supposed to have performed over a revolution and a half of the earth.
I place great confidence in the result obtained from the observations deduced from India, because there there are scores of trained meteorological observers whose duty it is to immediately report any phenomenon that may take place, and such as that concerning which I speak could not have escaped their immediate notice: so we may conclude that the hour of its arrival there is very accurately determined, which gives a mean diurnal velocity of 2,162 miles: and taking the velocity from its journey and a half round the world from India to lat. 24° N. and long. 140½° W., we find it to be 2,192 miles a day, or 30 miles only in excess of the other computation.
But if we take the whole journey from Krakatoa to that locality, about two and three-quarters revolutions round the globe, we find the mean to be 30 miles less than the first, or 2,132 miles, and this will be accounted for through the diminished value of the degree in longitude, at the mean latitude between Java and lat. 24° N.
The mean diurnal velocities obtained from the intermediate stations between Java and India agree very closely when we consider that at those several places the phenomenon was wholly unexpected, and thus, in most instances, the dates and times given appear to be somewhat late, it being quite possible and natural that it escaped notice at least once; in India, however, we may conclude that they were on the alert, and consequently the mean velocity deduced from that place ought to bear great weight. There is another thing that ought not to be lost sight of—viz., that without this list of stations, more than encircling the globe, one might suppose that the cloud after leaving Krakatoa stretched away westward, and as I gather from Lockyer' paper by his North-South line, to have extended to the north and south, forming a letter V with the apex at the Straits of Sunda. Now, Lockyer tracks it to Panama, to which place we see it to have had a diurnal velocity of 2,059 miles, and from Panama to India I made it 2,200 miles a day, which makes me believe that the cloud was performing a spiral path northwards round the globe.
Before proceeding I will now refer to the observations in the southern hemisphere in order to see whether the same has taken place there. This table has been prepared in like manner to the former—viz., the dates and times are reduced to that of Krakatoa, and the distances in English miles obtained from the difference in degrees of longitude reduced to the value of the mean latitude of the two places.
Table II., showing the Mean Diurnal Velocity in English Miles of the Phenomena of Coloured Suns and Brilliant Sunsets in the Southern Hemisphere:—
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|—||Time from Java to||Java.||Mauritius.||Adelaide.||C. of Good Hope.|
|Cape of Good Hope||24||2082||2047||2010|
Arithmetical mean = 2031 miles per diem.
True mean of 1st column = 2100 "
The marked similarity between these two tables is most striking, and, as in the first table, the greatest discrepancy is found between Krakatoa and Mauritius, where the time is reckoned in so many hours, in which case an hour or two makes a material difference in the diurnal velocity.
At present I cannot find any station reporting the phenomenon between Mauritius and Adelaide, but we may conclude that after it passed Mauritius it crossed Africa, the South Atlantic, and South America, whence we may expect to hear of it as there are many competent observers in that part of the world; it then traversed the great South Pacific Ocean and North Australia, and, after performing another such journey round the world, was seen at Adelaide in South Australia about the 17th September. I conclude, as Mr. Todd, the Government Astronomer there, says in his report to “Nature,” that it was visible during the last fortnight of September. We next hear of it at the Cape of Good Hope on the 20th September. It again crossed the South Atlantic and South America about the latitude of Buenos Ayres, and a third time traversed the South Pacific, striking the coast of New Zealand on the 25th September, the date of my first seeing it, on which occasion the western sky at sunset presented all the colours seen in the pearl shell. Since then the western and eastern skies have presented those beautiful crimson tints that have delighted and astonished the world, and on many occasions have I seen it almost in the zenith two hours after sunset. During some evenings it has quite illuminated the western face of buildings with a bright red glow, as from a fire, and on others it has been very faint and sometimes not discernible, giving to my mind the idea of its not being a continuous band, but a series of dust clouds with clear spaces between.
From an investigation of the two foregoing tables, it will be seen that the mean diurnal velocity in the northern hemisphere was, during the first revolution, about 2,162 miles, and during the second it increased to 2,192, or 30 miles per diem extra. And the same increased velocity is observed in the southern hemisphere, where we find the approximate velocity during the first two revolutions, viz., on its reaching Adelaide, to be 2,041, whereas during the next revolution from Adelaide round to New Zealand it was 2,120 miles, or an increase of 80 miles a day.
It will be further noticed that in the northern hemisphere the time occupied in its first revolution was about 11 days, and the same rate is observed during the next revolution and three-quarters—or, in other words, within the tropics it encircled the world in 11 days. It is the same within the southern tropics, where it took 21¼ days to reach Adelaide in its second revolution; but it performed the next revolution in about 9½ days, reaching New Zealand in 29¼ days after the eruption. Thus it performed two revolutions and three-quarters (2¾) in the northern hemisphere in 29⅔ days, and
in the southern hemisphere it performed two and seven-eighths (2⅞) revolutions in 29¼ days, showing that the initial velocity at starting has only very slightly fallen off in even latitude 45° south. So in the following discussion, I will adopt a mean diurnal velocity for the dust-cloud of 2,083 miles, or 87 miles an hour to the westward.
As I showed at the beginning that if the atmosphere be considered as part and parcel of the earth, a particle of it at a certain height will cover a greater distance in a certain time than that part of the earth immediately beneath would: so if we know the rate per hour that a certain thing apparently moves to the westward, or seems to lag behind the diurnal revolution, we can ascertain the height. We know that it lags behind at the rate of 2,083 miles a day, which added to the circumference of the world gives the circumference of a circle 26,908 miles ÷ 3.1416, gives a diameter of 8,565 miles, or 664 greater than that of the earth, or at a height of 332 miles above the surface. Or putting it this way,—we may assume that at the latitude of Krakatoa the earth has an hourly velocity of 1,034 miles, and that any matter ejected thence into the upper regions of the atmosphere would retain the same rotary velocity as it had before, viz., 1,034 per hour to the eastward; but we have material under our observation which cannot keep its zenithal position at starting, by 87 miles per hour, showing it to be at an elevation of 332 miles.
Now the spectroscope tells us that the red colour is produced through dust of almost ultra-microscopic fineness, and in some specimens of this dust that have already fallen, the microscope shows the existence of salt crystals, which fact in itself almost proves it to be of volcanic origin, and not meteoric or cosmic dust. Now Professor Helmholtz states that “the reflecting medium, whatever it was, over Berlin on the last three nights of November, was about 40 miles above the earth;” and if we work on these data, we have a circle whose diameter is 80 miles greater that of the earth, or a circle of 7,981 miles, which × 3.1416 gives a circumference of 25,073, or 248 miles more than that of the earth, which divided by 24 shows an excess of about 10⅓ miles per hour above the surface velocity of rotation. But we want to account for an excess of 87 miles per hour, so if we accept Professor Helmholtz' statement, we must only suppose that at the altitude of 40 miles there is an easterly current, or one moving to the westward, of 77 miles per hour. For, assuming as we do from the foregoing tables and calculations that the earth rolls from under the cloud at the rate of 87 miles per hour, and that, unless we admit of an easterly current, we cannot stop short of that enormous height of 332 miles, unless we suppose that the power of gravitation has only a feeble hold on those most minute dust particles at the altitude of 40 miles, where the air has not the many thousandth part of the density it has on the surface of the globe.
Mr. W. H. Preece writes, stating his opinion that the mass of matter ejected retained the same electric sign as that of the earth, and as long as that was the case the repulsion force would be sufficient to keep the matter afloat: and, in reference to that theory, Mr. Crookes writes to state that with the rarefaction of one millionth of the atmosphere, two pieces of electrified gold leaf repelled each other at a considerable angle for 13 months; and goes on to state that that rarefaction is attained at an altitude of 62 miles, and that the air there is a perfect non-conductor of statical electricity without interfering with the mutual repulsion of similarly electrified particles; and when we bear in mind that the particles of minute dust are many thousands of times smaller and lighter than the gold leaves operated upon, there is every reason to believe that electrified dust, even projected 50 or 60 miles high, might remain there many years.
Before proceeding further, I must draw your attention to the fact that at the time of the great eruption, and during September, the mean temperature at Batavia and throughout Java generally is at its maximum; consequently we may conclude that the equatorial belt of calms and uprushing air, that encircles the globe, was lying over that district at the time. This uprush is caused through the heated atmosphere rising and the two trade winds, the north-east and south-east, feed it. When this heated air has reached its proper altitude, it flows off to the north and south, but the rotation of the earth causes it to flow towards the north-east in the north hemisphere, and to the south-east in the south hemisphere, and these winds are called by some the return trades, and by others the south-west and north-west upper currents respectively, and are of great altitude, probably ranging up to 50,000 feet.
Well, the most bulky masses cast upward by the eruption of Krakatoa would immediately fall, and the less bulky would fall later, according to their size, but the great portion of the dust and ash would be caught, on its downward course, in those upper currents just alluded to, and be carried by them to the north-east and south-east. Such we find to be the fact, for the ship “Meda,” when to the westward of Cape North-west, Australia, or about 1,050 miles south-east of Krakatoa, experienced a fall of dust like fuller' earth, which covered the vessel, on the night of the 30th-31st August. And Captain Tierney of the brig “Hazard” on the 1st September, near New Britain and New Ireland, a distance of 3,850 miles due east of Krakatoa, saw the coloured sun, which was no doubt due to the presence of dust in the atmosphere drifted eastward with the upper current.
Now, turning to the north-east quarter, or the direction in which the south-west upper current of the north hemisphere proceeds, we find that in Japan during the 29th, 30th and 31st August, the sun was of a copper
colour and had no brightness in it. At Yokohama Mr. Hamilton states that on the 29th and 30th the sun was of a blood-red colour and appeared to be obscured. This is at a distance of about 3,000 miles from Krakatoa, which gives a velocity of the upper current, or return trade-wind, of about 62 miles per hour; this is not excessive, as I have often measured the velocity of the north-west upper current at Adelaide as over 80 miles per hour.
You may remember that I did not continue the tracking of the dust-cloud from that position assigned to it by Captain Penhallow, in lat. 24° N. long. 140½° W., on the 25th September, because the European and American reports are so peculiar. Apparently, it was seen in England before the rest of Europe, viz., on the 4th and 9th November, in California on the 20th, San Francisco 23rd, Italy 25th, New York 27th, and at Berlin on the 28th. So you see that the geographical arrangement is rather mixed in reference to the order of dates. This may be accounted for by the fact that there was a very severe volcanic eruption in the Alaska Group and Peninsula in October I think; it was very intense and quite capable of ejecting a dust-cloud that would envelope the polar and temperate regions of the northern hemisphere: of course it was not nearly so terrific as that of Krakatoa. So you will see that we must be careful before we assert that the brilliant sunsets of Europe are of Krakatoa origin.
The phenomena of coloured suns and brilliant sunsets, I may tell you, have been seen before, both in Europe and America, in connection with Vesuvian and Iceland outbursts. Mrs. Somerville, the famous geographer, gives an instance of them being seen in Norway, and traced their origin to a severe eruption in Iceland. And H. C. Russell, B.A., F.R.A.S., F.M.S., Government Astronomer, Sydney, in his book on the climate of New South Wales, pp. 187 and 188, gives some most interesting instances of historical accounts of darkened andcoloured suns. I will quote them in their chronological order:—
“At certain times the sun appears to be not of his wonted brightness, as it happened to be for a whole year when Cæsar was murdered, when it was so darkened that it could not ripen the fruits of the earth.” Virgil, Geor., Liber I., etc.
In 1090 there was a darkening of the sun for three hours.
In 1106, beginning of February, there was an obscuration of the sun.
In 1208 there was a darkening of the sun for six hours.
In 1547, 24th to 28th August, the sun was reddish, and so dark that several stars were visible at noonday.
In 1706, 12th May, about 10 o'clock in the morning it became so dark that bats commenced flying and persons were obliged to light candles.
In 1777, 17th June, about noon, Messier states he perceived an immense number of black globules pass over the sun' disc.
In 1783 there was a dry fog, and many attributed it to volcanic action, and it is well known that in February that year fearful earthquakes in Calabria took place, followed by a long list of volcanic eruptions in the world.
In 1831, there was an extraordinary dry fog, which excited public attention throughout the world. It appeared on the coast of Africa on the 3rd August; at Odessa, on the 9th August; in South France, on the 10th August; at Paris, on the 10th August; New York, on the 15th August; Canton (China), at the end of August. This fog was so thick that it was possible to observe the sun all day with the naked eye, and without a dark glass; and in some places the sun could not be seen till it was 15° or 20° high. At Algiers, United States, and Canton the sun' disc appeared of an azure blue, or of a greenish colour. Where the fog was dense, the smallest print could be read even at midnight.
In 1873, of the dry fog which came on suddenly in June, it is recorded that it extended from the northern coast of Africa, over France, to Sweden, and over great part of North America, and lasted more than a month. Travellers found it on the summits of the Alps. Abundant rain in June and July, and most violent winds did not dissipate it; and in some places it was so dense that the sun could not be seen until it had attained an altitude of 12°; and throughout the day-time it was red and so dull that it might be looked at with the naked eye. The fog diffused a disagreeable odour, and the humidity ranged from 57 to 68, while in an ordinary fog it is 100. It had a phosphorescent appearance, and the light at midnight was compared to that of full moon.
Here was exhibited a diagram VOL. XVII, pl. xix., drawn correctly to a scale of 50 miles to an inch, showing the arc (of 15°) of a circle whose radius was 6 feet 7 inches, or a diameter of 13 feet 2 inches. The Himalayas were shown in their correct proportion; so was the smoke from Cotopaxi, estimated by Whymper, while on Chimborazo, at 40,000 feet; he saw, at 5.45 a.m. of the 30th July, 1880, a dense column of smoke shot up straight into the atmosphere with prodigious velocity, which in less than one minute had risen 20,000 feet above the crater, giving the total height of 40,000 feet above sea-level. The dust, he goes on to state, fell on Chimborazo after six hours, and he estimated that each particle did not weigh the one-twenty-five-thousandth (½5000) part of a grain, and the finest were still lighter.
Some people—and very rightly too—express wonder and unbelief at the possibility of dust being capable of being shot up to such a height as that ascribed to it, as to cause the red sunsets, but here I have quoted the fact of such as seen by a man of known repute; the dust and ash were shot up to that great height; and not only that, but as the dust cloud came between Mr. Whymper and the sun, he saw the phenomenon of the coloured sun. The same may be seen during any very heavy dust storm anywhere, when the cloud is between the observer and the sun.
In this description, given by Whymper, we have a good illustration of the tremendous force Nature usesin these convulsions,—a force that could throw the finest dust to a height of 20,000 feet is almost inconceivable to the human mind,—and in that phenomenon we have, I may say, only an every day occurrence when compared with that giant eruption of Krakatoa. Let us draw a comparison: At the destruction of Pompeii, situated at the foot of Vesuvius, where the city was enveloped with darkness from the density of the dust and ash cloud that shrouded it, and that ultimately buried it;—but now contemplate the tremendous power that ejected from a mountain a sufficiency of dust and ash to envelope a city in total darkness for 36 hours, eighty miles distant. On that diagram I have sketched an imaginary picture of the eruption, and eighty miles distant is represented by a little over 1½; inch, where you see the letter B., showing to your mind the relative distance of Batavia from Krakatoa. You can form in your imagination some idea of the great height the dust cloud ascended: to my mind twice forty would not be too great. Then again we have the ship “Charles Bal,” which, when 30 miles distant, was enveloped at noon-day in pitch darkness through the mud-fall.
Furthermore, as Lockyer says, the sound, the least part of the affair, was heard over an area of 4,000 miles in diameter, viz., in Ceylon to the north-west, at Saigon to the north, and throughout North Australia to the south-east. In the last quarter, the reports were at 15 minutes' intervals, and sounded like ship guns, but as the hearers were from 150 to 200 miles from the coast, such cause could not be assigned. All that can be said is, that it is beyond the human mind to conceive of such gigantic forces, and therefore absurd to throw doubt on the result; by which I mean, that if the laws of refraction show that the substance, whatever it may be that causes the red glow, is at an altitude of 40 or 60 miles, it is ridiculous to doubt that result, when one cannot conceive the magnitude of the power that operated.
It was not only one eruption that took place, but several during the 26th, the following night, and up to 11.15 a.m. of the 27th, about which time the grand finale is supposed to have taken place. These eruptions
followed each other in rapid succession, and are thought to have been caused by the rapid conversion into steam of vast quantities of water that found admittance into the bowels of the earth. Later on, the influx of water was too much, and the result was that a tremendous power was generated, so much so as to cause the north part of the island to be blown away, and fall eight miles to the north, forming what is now called Steer' Island. This was followed by a still greater eruption, when it is thought that the north-east portion was blown clean away, passing over Long Island, and fell at a distance of seven miles, forming what is now known as Calmyer' Island. These suppositions are almost proved to be facts, from the marine survey of the Straits just concluded, from which it will be seen that the bottom surrounding these new islands has not been raised, which would most naturally have been the case had they been caused by upheaval; but if anything the bottom shows a slightly increased depth in the direction of the great pit that now occupies the position that the peak of Krakatoa did the day before. These incidents are cited to show you the awful nature and magnitude of the forces brought into play, so you can the more readily satisfy your minds as to the great height the dust and ash were thrown to.
As I said before, this dust-cloud may probably be denser in some parts than others, owing that fact to the relative period of time elapsed between each eruption; where it is dense we may assume that they followed each other rapidly, and where it is less dense the interval of time was greater. For you must remember that it was shown to you that the cloud apparently moves to the westward, or that the earth moves from beneath the cloud at the rate of 87 miles per hour, so that during each hour of the eruption there was a long streak of smoke and dust being formed. These densest parts were no doubt the cause of the coloured suns, and, as some observers state, “the sun appeared to shine with lessened strength,” others, “that it was rayless and giving no heat;” so we may look upon that dust-cloud as playing the part of a great screen, shutting off some of the heat of the sun from us.
In these southern latitudes we have experienced those brilliant sunsets for over seven months, and I have no hesitation in expressing my opinion that the remarkably cool and wet summer just passed in New Zealand was due to that dust-cloud shutting off the sun' heat in a great degree. And I see from the Adelaide report that the mean temperature there during January was over 4½ degrees cooler than the average of the previous twenty-five years, and on only one occasion during that period was it so low, viz., in 1869. At Melbourne also the weather was more like winter than summer. Whereas in North and Central Australia, or I may say down to latitude 30°
in that continent, the weather was fine, clear, hot without rain, giving me the idea that the sun had less power than usual, consequently the north-west monsoon was very feeble, not penetrating far inland, the result being that the interior of Australia has undergone one of the most disastrous droughts on record. But now that, as we may suppose, the equatorial regions of the atmosphere have parted with the greater part of their dust, if not all, the sun has regained his usual power, and the north-west monsoon its usual strength, penetrating the heart of Australia with refreshing rains and thunderstorms. So we have here an instance of a most terrific phenomenon that not only brought death and destruction to thousands at the time, but that indirectly caused the death of thousands and thousands of cattle through drought; and it would be most interesting and instructive to learn whether or not such consequences were experienced in other parts of the southern hemisphere.
It would be beyond the province of this paper to enter on a history of the tidal and atmospheric waves that resulted from this eruption, but I will state two facts to finally clinch your mind of its magnitude. When the earth opened her mouth and swallowed that vast quantity of water the down-rush that accompanied the closing-in of the surrounding crust was so much as to produce a tidal wave that passed and repassed twice, I believe, round the globe. The other fact is, that the tremendous explosion that accompanied the final eruption produced such a vacuum as to cause atmospheric waves to start, and which traversed and retraversed the earth to the antipodes of Java no less than four times. Some astronomers have thought that the whole phenomenon may be accounted for by supposing the earth to be passing through a dense meteoric track. To my mind, however, the greatest difficulties brought to bear against the volcanic theory are child' play when compared with the possibility, about ten thousand millions to one, of a meteoric track so formed as to have its path, either at perihelion or aphelion, so remarkably co-incident with that of the earth as to keep company with her for seven or eight months. Besides, if it were either meteoric or cosmic dust it would have been seen all over the earth at the same time and would be visible all night. No, the only extra-terrestrial argument that would bear investigation is that of its belonging to the phenomenon of the zodiacal light, which argument, I believe, was adopted by my friend Charles Todd, of Adelaide, at first; but, as time goes on and more information is gathered, the volcanic theory, I believe, will be finally accepted.