Every reader of this book has heard of the Aurora Borealis, or Northern Lights, and the Aurora Australis, or Southern Lights. Some readers may have visited Norway and gone far enough to catch a glimpse of this mysterious phenomenon. We say mysterious because scientists have never been able to explain it, although they usually try to do so by saying something indefinite about the earth's electricity and magnetism. We claim, on the basis of our theory, to explain definitely what causes the auroral lights: that the central sun, flashing its beams through the polar openings, is the cause. To enforce this claim we shall first describe. in the words of competent observers, just what these lights look like and how they behave. We shall then show--also on the best scientific evidence--that they are not and could not be caused by electricity or magnetism; we shall refute many fallacies on that subject. And then we shall give abundant evidence proving that the reflection of the rays of the central sun by the earth's atmosphere, modified by the conditions, cloudy or otherwise, of the atmosphere of the interior of the earth, is what causes these wonderful displays of light.
We shall have more than one description of the aurora in the following chapter, but perhaps it will be interesting to start our enquiry from a rather old but very good book to which we have referred before. In Honorable Daines Barrington's "Possibility of Approaching the North Pole" he asks a correspondent about the aurora and is assured that it "is commonly seen most strong in the north and is very red and fiery."
Greely in his "Three Years of Arctic Service" says a number of interesting things. He remarks that there is always a feeble auroral light even when there is not a brilliant display. Soon after that remark we find him observing a perfectly circular aurora which he calls a mock sun. It had burning colors of blue, yellow and red with bars of white. A few days after, he witnessed an aurora which had a beautiful corona or crown of light around it. It had numerous and brilliant streamers. Then here is another description of an aurora:
"A beautiful and brilliant arch about three degrees wide, formed of twisted, convoluted bands of light, similar to twisted ribbons, extended from the south-west through the zenith to the north-eastern horizon. Occasionally, well-marked and clearly defined patches of light detached themselves, as puffs of smoke from a pipe, and drifted fading to the northwest.
[paragraph continues] The arch seemed to be continually renewing itself from the southwest to fade at the opposite end. Perhaps a better idea of this peculiar formation may be conveyed by likening the display to an arch having the appearance of an endless, revolving screw. This formation was by no means infrequent, but I have never seen it elsewhere or known it to be described."
Again Greely writes:
"A particularly fine aurora, like a pillar of glowing fire, from horizon to horizon through the zenith, showing at times a decidedly rosy tint."
It will at once strike the reader how well these observations fit in with our theory that the aurora is the reflection of the beams of the inner sun coming through the polar orifice, when he remembers the extraordinary differences there will be in the conditions which from time to time modify those reflections. There may be clouds between the inner sun and the polar orifice, and these may be diffused or in heavy dense masses. The atmosphere may be moister or dryer at one time than another and this will modify the reflections. The earth's outer atmosphere may vary as well as its inner one. Hence all the differences which are described in the succeeding pages.
Let us now take the testimony of Fridtjof Nansen on the subject of the aurora. In "Farthest North"
he describes many appearances of this marvel. Here is part of one of his descriptions:
"A lovely aurora this evening. A brilliant corona encircled the zenith with a wreath of streamers in several layers, one outside the other; then larger and smaller sheaves of streamers over the sky. . . . . . . All of them, however, tended upward toward the corona, which shone like a halo. Every now and then I could discern a dark patch in its middle, at the point where all the rays converged. It lay a little south of the pole star, and approached Cassiopeia in the position it then occupied. But the halo kept smouldering and shifting just as if a gale in the upper strata of the atmosphere were playing the bellows to it. Presently fresh streamers shot out of the darkness out-side the inner halo, followed by other bright shafts of light in a still wider circle, and meanwhile the dark space in the middle was clearly visible; at other times it was completely covered with masses of light. Then it appeared as if the storm abated, and the whole turned pale, and glowed with a faint whitish hue for a little while, only to shoot wildly up once more and to begin the same dance over again. Then the entire mass of light around the corona began to rock to and fro in large waves over the zenith and the dark central point, whereupon the gale seemed to increase and whirl the streamers into an inextricable tangle, till they merged into a luminous vapor
that enveloped the corona and drowned it in a deluge of light, so that neither it nor the streamers, nor the dark centre could be seen--nothing, in fact, but a chaos of shining mist."
Now it is obvious that the real explanation of this phenomenon is to be found in those words which Nansen uses without seeing their real bearing on the problem: "it appeared as if the storm abated" and "the gale seemed to increase". As a matter of fact the light from the central sun was being reflected from the higher reaches of the earth's atmosphere and the reflection was interfered with by a violent storm in the interior of the earth. Clouds were rapidly being formed and being dissipated in that part of the interior near the polar, opening. Thus the rays of the central sun were one moment permitted to pass without obstruction; then the opening would be clouded up, at first perhaps by one dense cloud giving the central dark spot in the reflection of which Nansen speaks; then there would be a general filming over of the aperture and the result would be a diffused reflection.
Not only is it true that no other explanation fits the facts of the rapid changes without apparent cause, but Nansen himself acknowledges that he was quite ignorant of the cause of the phenomenon. He says:
"O thou mysterious radiance! What art thou and
whence comest thou? Yet why ask? . . . . . What would it profit if we could say that it is an electric discharge or currents of electricity through the upper regions of the air, and were able to describe in minutest detail how it all came to be?"
The reader will notice that Nansen does not commit himself to the popular view that the aurora is caused by electricity. In that he shows his wisdom, for we shall now deduce evidence to show that electricity has nothing whatever to do with the aurora.
If, as some people think, the earth's magnetism or electricity at the polar regions or around the earth's magnetic poles were the cause of the aurora, there would be a constant relation between its displays and the different instruments which have been constructed to tell the presence of magnetism and electricity--the compass would be affected and the electrometer would be affected. And there would certainly not be the irregularity about these displays that Nansen describes above. So now let us take the testimony of other observers. Payer who entered the Arctic circle on the "Tegetthoff" during the years 1872-1874, has a whole chapter devoted to the aurora. He says that it is very difficult to characterise the forms of this phenomenon, not only because they are manifold but because they are constantly changing. Sometimes there are brilliant
bands and patches of light upon the sky, sometimes there are appearances like "glowing balls of light". He further says:
"The movement of the waves of light gave the impression that they were the sports of winds, and their sudden and rapid rise resembled the uprisings of whirling vapors, such as the geysers might send forth In many cases the aurora much resembled a flash of summer lightning conceived as permanent".
Now that description precisely fits in with what we have described as the reflection of the light of the central sun, that light being by turns cut off in one part and then another, here and there a gleam breaking through, as the atmosphere of the interior changed. That the appearance was "the sport of winds," as Payer says, is literally true, only the winds were those shifting the clouds in the atmosphere on the inner side of the polar orifice. And it may be noted that a magnetic display could not be the sport of winds, for wind does not effect the ether in which medium along magnetic lines of force and electrical light from discharges work. If the aurora were caused by electrical lines of force discharging themselves in light, it would not be so capricious as described above. It would be a more or less steady appearance.
Payer goes on to say that often after a brilliant aurora there would be bad weather which certainly sounds as if the storm clouds from which it was reflected from the inner sun were breaking, or perhaps a storm starting in the interior was coming over the lip and running its course in the Arctic circle. He adds that none of the theories current at the time explain the phenomenon. He thinks, however, that vapors rather than electricity may play a part in the phenomenon, especially on account of its "indefinite form" which, as we have pointed out above,
is only explicable on our showing that the aurora is the reflection of the central sun and not due to any electrical discharge. A member of Payer's expedition, Lieutenant Weyprecht, describes one form of the aurora as an arch of light, looking as if "it were the upper limit of a segment of a circle and it is often thrice the breath of a rainbow. Often as it rises other arches follow it, all rising toward the zenith." Now we know that a rainbow is caused by the sun that lights the earth, and it is only natural that when the conditions are calm the reflection of the inner sun should also take this form--the circularity of the arch of the aurora simply being the reflection of the circular outline of that inner sun's diameter. Payer quotes Parry as saying that there was no magnetic disturbance when the aurora was
seen. He, himself, is not able to make any connection between variations of the magnetic instruments and the presence of the aurora, although he tries hard to do so. As the final result of his observations he writes as follows:
"No pencil can draw it, no colors can paint it, and no words can describe it in all its magnificence. And here below stand we poor men and speak of knowledge and progress, and pride ourselves on the understanding with which we extort from Nature her mysteries. We stand and gaze on the mystery which Nature has written for us in flaming letters on the dark vault of night, and ultimately we can only wonder and confess that, in truth, we know nothing of it."
Now some day that will appear very pessimistic, for we are making progress in knowledge, and about this very subject. After the enthusiastic description which Payer gives of the beauties of the aurora, might it not have occurred to him that magnetic or electrical discharges could not produce such grandeur because electrical flashes are only bright when the electricity is at a very high tension. But as soon as the tension of the electricity in the atmosphere becomes great enough we have a thunder storm, and we all know just how bright the lightning flash is. But how about these marvelous colors, this sea of flames of which Payer says "is that sea red, white or green? Who can say?" And Payer admits that
it is even impossible to tell whether the "rays shoot from above downward or from below upward." Such colors could not possibly be produced by electricity; they are the colors of the interior sun partly split up like the rainbow by their breaking up as they pass from stratum to stratum of the atmosphere at length to be reflected back to us.
But we have denied that these displays have any effect on the magnetic needle or the electrometer. Let us verify that assertion by evidence more powerful than Payer's. Greely says in the book from which we have already quoted that "it seems to be the experience here that the magnet is undisturbed during the prevalence of colorless auroras" although he did observe in a few cases he reports that magnetic storms took place at about the same time as there were auroral displays. In these cases, however, it is certain that the conditions which produced the stormy and colored appearance of the aurora due to its refraction through damp air--also produced the magnetic storms, just as in our own latitudes an electrical storm is accompanied by a great deal of moisture in the air. While in ordinary weather, the atmosphere being uniform throughout, the auroral reflection is uncolored because it is not broken up into a spectrum and at the same time in such uniformly dry air there is nothing to cause a magnetic storm. But it by no means follows, from the fact that Greely saw these magnetic storms upon one or
two occasions, that they always accompany colored auroras, for as a matter of fact they do not, as our further testimony shows.
But there is one important preliminary point. If the aurora is a reflection of the inner sun, it will only be on the rare occasions when the whole polar orifice is covered with cloud--and how rare such a condition would be, even in the damp atmosphere of the interior--that the aurora will be absent. The sun is always there, the orifice is always there, and the earth's atmosphere above the polar regions will always be dense enough to reflect some light, though not of course dense enough to reflect the wonderful lights that it sometimes does. So, if our theory be true, there ought always to be some auroral light at the pole. And we have the testimony of the celebrated French astronomer, Camille Flammarion, that this is so. In one place in his book, "The Atmosphere", he says: "Nearly every night there is a more or less brilliant display of these auroral lights". And later in the same book he says: "This light of the earth, the emission of which toward the poles is almost continuous. . . . . ."
And now for the alleged disturbance of the magnet or other instruments. In Sargent and Cunning-ham's "Wonders of the Arctic World," which is a carefully written account of the earlier expeditions,
it is recorded that during the Second Land Expedition of Franklin, enough observations of the aurora were made with specially designed instruments and recorded to establish the fact that no disturbances of the magnetic needle accompanied the displays. (Page 164.)
We may corroborate this testimony by referring to "Wonders of the Polar World", by Herman Dieck, M. A., another work in which the main results of polar exploration are summarized. Mr. Dieck quotes a description of an aurora seen by Greely's men, in which the arch form which we have already described was very prominent, and also the prismatic colors showing that the aurora was colored through the breaking up of sunlight, just as in the case of the rainbow. And he adds that there was no noise--this is important, as electrical discharges are always accompanied by a crackling noise--and there was no disturbance of the compass. Later, Lieutenant Greely set up an electrometer, an instrument which records the presence of very small amounts of electricity, but "to his astonishment" there was not a trace of electrical disturbance. Greely also noticed that there were no crackling sounds in connection with the display.
It is often the case that once the real explanation of anything is found out, we get corroborative evidence from the most unexpected sources, and the
reader who turns to a very recent and most depend-able work in the Home University Library, that of William S. Bruce, leader of the Scottish National Antarctic Expedition, called "Polar Exploration", will find just such testimony. Professor Bruce says that the phenomenon occurs in other planets than our own and that it has been notably observed in Venus--which of course would be the case as the reader will remember that Venus occasionally shows us her central sun, and so we would naturally expect also to see its reflection in Venus' atmosphere. Professor Bruce also tells us that the early Norwegians held that the aurora was due to "fires which surround the sea to the north". Now that is very interesting because it suggests that perhaps these people had had in some way communication with the interior of the earth, and they might easily have thought that the central sun was some sort of fire. In fact some of them thought that the aurora was simply "a reflection of the sun when it is below the horizon" and that suggests that they had actually got far enough north to see the interior sun for a short time, perhaps, and that they afterwards saw its reflection in the sky in the form of an aurora, and remembering that they had just left the sun behind, they guessed that the two had this connection.
On the other hand, Professor Bruce quotes the observations of a British Antarctic Expedition to the effect that:
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The central sun as it would appear to an explorer when he had reached the spot indicated by the letter ''D'' on the diagram, if the atmospheric conditions were favorable.
"The observations of atmospheric electricity taken during the displays reveal no special effect due to the aurora."
There are some other considerations which show that the aurora is really due to the interior sun. Dr. Kane, in his account of his explorations, tells us that the aurora is brightest when it is white. That shows that when the reflection of the sun is so clear that the total white light is reflected, we get a much brighter effect than when the light is cut up into prismatic colors. In the latter case the atmosphere is damp and dense--that being the cause of the rainbow effect--and through such an atmosphere one cannot see so much. Hence the display is not so bright as it is when the atmosphere is clear and the light not broken up.
Again, if the aurora is the reflection of the central sun, we should expect to see it fully only near the polar orifice, and see only faint glimpses of its outer edges as we went further south. And that is precisely what is the actual fact of the matter. Says Dr. Nicholas Senn in his book "In the Heart of the Arctics":
"The aurora, which only occasionally is seen in our latitudes, is but the shadow of what is to be seen in the polar regions."
And in "Earth, Sea, and Sky," by H. D. Northrop, we read:
"As we retire from the pole, the phenomenon becomes a rare occurrence, and is less perfectly and distinctly developed."
Regarding the two quotations just made a word of explanation is necessary. When Dr. Senn speaks of the aurora being only a "shadow" when it is seen some distance south he does not mean that it is a shade. He simply means that it is much fainter than when it is seen in the north. Now what is the reason of this? It is well known that certain laws of refraction of light cause a very bright rainbow to cast another rainbow, similar to itself at a distance from itself in the sky. Sometimes when the rainbow is very bright there is enough light being refracted so that two reflections are formed, and then the first reflection is paler than the original rainbow and the second reflection is still paler. Similarly, the auroral light is refracted in part so that a faint image of it or "shadow" is seen rather far to the south, sometimes as far south as the latitude of Illinois. But it is well known that no aurora or reflection of an aurora is ever seen at the equator, and as the aurora which is seen some distance from the north is only a shadow or reflection of the real aurora it is only occasionally, when the atmosphere happens to be right for it, that we see this phenomenon.
H. D. Northrop further notes that the light of the aurora is continuous during the Arctic night, and he says that the arch which we have already mentioned as being such a prominent feature of the aurora is only "part of a ring of light which is elevated considerably above the surface of our globe, and whose center is situated in the vicinity of the pole."
And that is precisely what we should expect when we remember that it is the reflection of the rays coming through the polar orifice which causes the phenomenon. Northrop points out that a person looking at this ring from a point very far north would imagine that the aurora was to the south of him simply because the ring was so far spread out overhead.
This point is corroborated by the author of "The Arctic World" who says the same thing about the aurora. Meanwhile we find that William Denovan in his scientific reference work, "The Phenomena of Nature", makes the statement that:
"In temperate regions the aurora does not present such grand forms as in the extreme north."
The same author also makes another interesting point that supports our contention. It is that the corona or crown of light surrounding the sun is very like the light that the aurora gives us, and Nansen, in the second volume of his "Farthest North," speaks of
an aurora in which there was a reflection that looked very like a corona. But, the reader may say, that is only a chance resemblance. It might be thought so, but exact observation confirms the idea that the light is the same in both cases. Taylor Reed, writing in Popular Astronomy for 1895, describes the spectroscopic observation of the sun's corona and compares the result with the examination of the earth's aurora. He says:
"Both have their beautiful streams. Each has a characteristic form in the neighborhood of the pole of its sphere. Apply the spectroscope to each and the analogy is continued. Each gives in the spectrum an unidentified bright line, with fainter companions. Each shows a faint continuous spectrum.
We cannot imagine what further proof than the above anybody could need. If the two sorts of light give precisely the same spectroscopic appearances they must come from precisely similar sources. That is to say, if the corona is light caused by a sun, the aurora must also be light caused by a sun. And that is what we claim.
Let us, before concluding, however, give one or two more citations to show that the evidence already adduced is not only to be had in isolated instances but is agreed with by all observers at all times. In the first place, verification of the fact that Greely obtained
no results when he set up his electrometer during a display of the aurora when he was on his northern expedition, will be found in the interview which he gave the Associated Press and which was published all over the country and 'is to be found in the Scientific American Supplement for September 6, 1884. Again, Nordenskiold gave a correspondent of the New York Herald an account of his explorations in the Arctic in the course of which he made this very important announcement:
"Whenever the sky was clear, and there was no sun or moon, he saw constant in the northeast horizon, and almost always in the same exact spot, a faintly luminous arc so motionless as to be susceptible of accurate measurement. This phenomenon, Nordenskiold concludes, comes from an actual aureole, or ring of light, surrounding the northern portion of the globe."
It is notable that Nordenskiold also says that there were no very brilliant displays that year. Evidently the weather was calm, there were no storms to make rapidly changing reflections, and as the air in the interior was probably laden with moisture the display was not brilliant. But the fact it was circular and steady shows that it was a reflection of a body that was also circular and steady, and reflected through a circular opening, and that body was no less than the interior sun.
It is interesting to note that the idea that the
aurora is a reflection of sunlight is not confined to those old Norwegians we have spoken of. In an article translated from "La Lumiere Electrique" by the Scientific American Supplement for February 17, 1883, we are told that Descartes, Ellis, Frobisher, Franklin, Raspail and Wolfert, all thought that the aurora was from sunlight. They were near the truth, but they did not know what sun it really was that caused the light. In this same article we are told that the aurora is only seen at the pole and that any celestial light seen in the skies at lower latitudes---such as the zodiacal light is not due to the aurora at all.
In Nature, the volume of 1878, will be found an account of the eclipse of the sun as observed by the astronomer royal of Great Britain wherein it is stated that Professor Bass observed steadily for the whole period one part of the sun's corona, and he found that it pulsated in just the same manner as the aurora does.
And in conclusion we may repeat the observation of Payer, quoted also by W. J. Gordon in his book "Round About the North Pole", that it is impossible to discover whether the rays of the aurora shoot upward or downward. If those rays were electrical discharges they would all be going in the same direction, like the lines of force from a magnet. But
the very fact that these rays are confused and seem to go now one way and now another, shows that they are light reflections which cross one another and appear and disappear as the reflecting surface--the upper layers of the atmosphere--varies. Thus we have one more item of the cumulative proof that the aurora is not a magnetic or electrical disturbance but simply a dazzling reflection from the rays of the central sun. And our next task is to see if there are not evidences of life in the land that is warmed by that sun. For if it warms continents and waters in the interior of the earth, if, as we have seen, birds have their feeding and breeding grounds there, if an occasional log or seed or pollen like dust is seen in the Arctic that come from some such unknown place as we have described, it ought to be possible to obtain enough evidence of such life as would prove up to the hilt the contention of this book.