The new star was first seen by Professor Schmidt, who has had the good fortune of announcing to astronomers more than one remarkable phenomenon. It was he who discovered in November 1866 that a lunar crater had disappeared, an announcement quite in accordance with the facts of the case. We have seen that he was one of the independent discoverers of the outburst in the Northern Crown. On November 24, at the early hour of 5.41 in the evening (showing that Schmidt takes time by the forelock at his observatory), he noticed a star of the third magnitude in the constellation of the Swan, not far from the tail of that southward-flying celestial bird. He is quite sure that on November 20, the last preceding clear evening, the star was not there. At midnight its light was very yellow, and it was somewhat brighter than the neighbouring star Eta Pegasi, on the Flying Horse's southernmost knee (if anatomists will excuse my following the ordinary usage which calls the wrist of the horse's fore-arm the knee). He sent news of the discovery forthwith to Leverrier, the chief of the Paris observatory; and the observers there set to work to analyse the light of the stranger. Unfortunately the star's suddenly acquired brilliancy rapidly faded. M. Paul Henry estimated the star's brightness on December 2 as equal only to that of a fifth-magnitude star. Moreover, the colour, which had been very yellow on November 24, was by this time 'greenish, almost blue.' On December 2, M. Cornu, observing during a short time when the star was visible through a break between clouds, found that the star's spectrum consisted almost entirely of bright lines. On December 5, he was able to determine the position of these lines, though still much interrupted by clouds. He found three bright lines of hydrogen, the strong (really double) line of sodium, the (really triple) line of magnesium, and two other lines. One of these last seemed to agree exactly in position with a bright line belonging to the corona seen around the sun during total eclipse.[35]
The star has since faded gradually in lustre until, at present, it is quite invisible to the naked eye.
We cannot doubt that the catastrophe which befell this star is of the same general nature as is that which befell the star in the Northern Crown. It is extremely significant that all the elements which manifested signs of intense heat in the case of the star in the Swan, are characteristic of our sun's outer appendages. We know that the coloured flames seen around the sun during total solar eclipse consist of glowing hydrogen, and of glowing matter giving a line so near the sodium line that in the case of a stellar spectrum it would, probably, not be possible to distinguish one from the other. Into the prominences there are thrown from time to time masses of glowing sodium, magnesium, and (in less degree) iron and other metallic vapours. Lastly, in that glorious appendage, the solar corona, which extends for hundreds of thousands of miles from the sun's surface, there are enormous quantities of some element, whose nature is as yet unknown, showing under spectroscopic analysis the bright line which seems to have appeared in the spectrum of the flaming sun in the Swan.
This evidence seems to me to suggest that the intense heat which suddenly affected this star had its origin from without. At the same time, I cannot agree with Meyer and Klein in considering that the cause of the heat was either the downfall of a planetary mass on the star, or the collision of the star with a star-cloudlet, or nebula, traversing space in one direction while the star swept onwards in another. A planet could not very well come into final conflict with its sun at one fell swoop. It would gradually draw nearer and nearer, not by the narrowing of its path, but by the change of the path's shape. The path would, in fact, become more and more eccentric; until, at length, at its point of nearest approach, the planet would graze its primary, exciting an intense heat where it struck, but escaping actual destruction that time. The planet would make another circuit, and again graze its sun, at or near the same part of the planet's path. For several circuits this would continue, the grazes not becoming more effective each time, but rather less. The interval between them, however, would grow continually less and less. At last the time would come when the planet's path would be reduced to the circular form, its globe touching its sun's all the way round, and then the planet would very quickly be reduced to vapour, and partly burned up, its substance being absorbed by its sun. But all the successive grazes would be indicated to us by accessions in the star's lustre, the period between each seeming outburst being only a few months at first, and becoming gradually less and less (during a long course of years, perhaps even of centuries), until the planet was finally destroyed. Nothing of this sort has happened in the case of any so-called new star.
As for the rush of a star through a nebulous mass, that is a theory which would scarcely be entertained by any one acquainted with the enormous distances separating the gaseous star-clouds properly called nebulæ. There may be small clouds of the same sort scattered much more densely through space; but we have not a particle of evidence that this actually is the case. All we certainly know about star-cloudlets suggest that the distances separating them from each other are comparable with those which separate star from star, in which case the idea of a star coming into collision with a star-cloudlet, and still more the idea of this occurring several times in a century, is wild in the extreme.
On the whole, the theory seems more probable than any of these, that enormous flights of large meteoric masses travel around those stars which thus occasionally break forth in conflagration, such flights travelling on exceedingly eccentric paths, and requiring enormously long periods to complete each circuit of their vast orbits. In conceiving this, we are not imagining anything new. Such a meteoric flight would differ only in degree not kind from meteoric flights which are known to circle around our own sun. I am not sure, indeed, that it can be definitely asserted that our sun has no meteoric appendages of the same nature as those which, if this theory be true, excite to intense periodic activity the sun round which they circle. We know that comets and meteors are closely connected, every comet being probably (many certainly) attended by flights of meteoric masses. The meteors which produce the celebrated November showers of falling stars follow in the track of a comet invisible to the naked eye. May we not reasonably suppose, then, that those glorious comets which have not only been visible but conspicuous, shining even in the day-time, and brandishing round tails which, like that of the 'wonder in heaven, the great dragon,' seemed to 'draw the third part of the stars of heaven,' are followed by much denser flights of much more massive meteors? Now some among these giant comets have paths which carry them very close to our sun. Newton's comet, with its tail a hundred millions of miles in length, all but grazed the sun's globe. The comet of 1843, whose tail, says Sir J. Herschel, 'stretched half-way across the sky,' must actually have grazed the sun, though but lightly, for its nucleus was within 80,000 miles of his surface, and its head was more than 160,000 miles in diameter. And these are only two among the few comets whose paths are known. At any time we might be visited by a comet mightier than either, travelling on an orbit intersecting the sun's surface, followed by flights of meteoric masses enormous in size and many in number, which, falling on the sun's globe with the enormous velocity corresponding to their vast orbital range and their near approach to the sun—a velocity of some 360 miles per second—would, beyond all doubt, excite his whole frame, and especially his surface regions, to a degree of heat far exceeding what he now emits.
We have had evidence of the tremendous heat to which the sun's surface would be excited by the downfall of a shower of large meteoric masses. Carrington and Hodgson, on September 1, 1859, observed (independently) the passage of two intensely bright bodies across a small part of the sun's surface—the bodies first increasing in brightness, then diminishing, then fading away. It is generally believed that these were meteoric masses raised to fierce heat by frictional resistance. Now so much brighter did they appear, or rather did that part of the sun's surface appear through which they had rushed, that Carrington supposed the dark glass screen used to protect the eye had broken, and Hodgson described the brightness of this part of the sun as such that the part shone like a brilliant star on the background of the glowing solar surface. Mark, also, the consequences of the downfall of those two bodies only. A magnetic disturbance affected the whole frame of the earth at the very time when the sun had been thus disturbed. Vivid auroras were seen not only in both hemispheres, but in latitudes where auroras are very seldom witnessed. 'By degrees,' says Sir J. Herschel, 'accounts began to pour in of great auroras seen not only in these latitudes, but at Rome, in the West Indies, in the tropics within eighteen degrees of the equator (where they hardly ever appear); nay, what is still more striking, in South America and in Australia—where, at Melbourne, on the night of September 2, the greatest aurora ever seen there made its appearance. These auroras were accompanied with unusually great electro-magnetic disturbances in every part of the world. In many places the telegraph wires struck work. They had too many private messages of their own to convey. At Washington and Philadelphia, in America, the electric signal-men received severe electric shocks. At a station in Norway the telegraphic apparatus was set fire to; and at Boston, in North America, a flame of fire followed the pen of Bain's electric telegraph, which writes down the message upon chemically prepared paper.' Seeing that where the two meteors fell the sun's surface glowed thus intensely, and that the effect of this accession of energy upon our earth was thus well marked, can it be doubted that a comet, bearing in its train a flight of many millions of meteoric masses, and falling directly upon the sun, would produce an accession of light and heat whose consequences would be disastrous? When the earth has passed through the richer portions (not the actual nuclei, be it remembered) of meteor systems, the meteors visible from even a single station have been counted by tens of thousands, and it has been computed that millions must have fallen upon the whole earth. These were meteors following in the train of very small comets. If a very large comet followed by no denser a flight of meteors, but each meteoric mass much larger, fell directly upon the sun, it would not be the outskirts but the nucleus of the meteoric train which would impinge upon him. They would number thousands of millions. The velocity of downfall of each mass would be more than 360 miles per second. And they would continue to pour in upon him for several days in succession, millions falling every hour. It seems not improbable that, under this tremendous and long-continued meteoric hail, his whole surface would be caused to glow as intensely as that small part whose brilliancy was so surprising in the observation made by Carrington and Hodgson. In that case, our sun, seen from some remote star whence ordinarily he is invisible, would shine out as a new sun, for a few days, while all things living on our earth, and whatever other members of the solar system are the abode of life, would inevitably be destroyed.
The reader must not suppose that this idea has been suggested merely in the attempt to explain outbursts of stars. The following passage from a paper of considerable scientific interest by Professor Kirkwood, of Bloomington, Indiana, a well-known American astronomer, shows that the idea had occurred to him for a very different reason. He speaks here of a probable connection between the comet of 1843 and the great sun-spot which appeared in June 1843. I am not sure, however, but that we may regard the very meteors which seem to have fallen on the sun on September 1, 1859, as bodies travelling in the track of the comet of 1843—just as the November meteors seen in 1867–8, 9, etc., until 1872, were bodies certainly following in the track of the telescopic comet of 1866. 'The opinion has been expressed by more than one astronomer,' he says, speaking of Carrington's observation, 'that this phenomenon was produced by the fall of meteoric matter upon the sun's surface. Now, the fact may be worthy of note that the comet of 1843 actually grazed the sun's atmosphere about three months before the appearance of the great sun-spot of the same year. Had it approached but little nearer, the resistance of the atmosphere would probably have brought its entire mass to the solar surface. Even at its actual distance it must have produced considerable atmospheric disturbance. But the recent discovery that a number of comets are associated with meteoric matter, travelling in nearly the same orbits, suggests the inquiry whether an enormous meteorite following in the comet's train, and having a somewhat less perihelion distance, may not have been precipitated upon the sun, thus producing the great disturbance observed so shortly after the comet's perihelion passage.'
There are those, myself among the number, who consider the periodicity of the solar spots, that tide of spots which flows to its maximum and then ebbs to its minimum in a little more than eleven years, as only explicable on the theory that a small comet having this period, and followed by a meteor train, has a path intersecting the sun's surface. In an article entitled 'The Sun a Bubble,' which appeared in the 'Cornhill Magazine' for October 1874, I remarked that from the observed phenomena of sun-spots we might be led to suspect the existence of some as yet undetected comet with a train of exceptionally large meteoric masses, travelling in a period of about eleven years round the sun, and having its place of nearest approach to that orb so close to the solar surface that, when the main flight is passing, the stragglers fall upon the sun's surface. In this case, we could readily understand that, as this small comet unquestionably causes our sun to be variable to some slight degree in brilliancy, in a period of about eleven years, so some much larger comet circling around Mira, in a period of about 331 days, may occasion those alternations of brightness which have been described above. It may be noticed in passing, that it is by no means certain that the time when the sun is most spotted is the time when he gives out least light. Though at such times his surface is dark where the spots are, yet elsewhere it is probably brighter than usual; at any rate, all the evidence we have tends to show that when the sun is most spotted, his energies are most active. It is then that the coloured flames leap to their greatest height and show their greatest brilliancy, then also that they show the most rapid and remarkable changes of shape.