Still, there remained something more to be determined. The existence of the photosphere being proved, the question arose—was there nothing beyond? or did it end abruptly? and this could only be determined at the period of a total eclipse, at the very moment when the obscuration of the sun being greatest, our atmosphere ceases to be illuminated. Hence the interest felt in an eclipse of the sun of late years.
In July 1842, at a total eclipse of the sun visible in several parts of the continent, the astronomers noticed, just as the sun was hidden by the moon, certain objects, in the form of rose-coloured protuberances, about two or three minutes high, astronomically speaking, projected from the surface of the moon. These appearances were variously explained: some supposed them to be lunar mountains; others saw in them effects of refraction or diffraction; but no precise explanation could be given; and mere guesses cannot be accepted as science. Others, again, thought them to be mountains in the sun, the summits stretching beyond the photosphere; but at the most moderate calculation, their height would have been about 60,000 miles—an elevation which, as is said, the solar attraction would render impossible. Another hypothesis was, that they were clouds floating in a solar, gaseous atmosphere.
M. Arago considers the last as the true explanation: it remained the great point to be proved. If it could be ascertained, that these red protuberances were not in actual contact with the moon, the demonstration would be complete. Speculation was busy, but nothing could be done in the way of verification until another eclipse took place. There was one in August 1850 total to the Sandwich Islands, at which, under direction of the French commandant at Tahiti, observations were made, the result being that the red prominences were seen to be separated by a fine line from the moon's circumference. Here was an important datum. It was confirmed by the observations of July 1851, by observers of different nations at different localities, who saw that the coloured peaks were detached from the moon; thus proving that they are not lunar mountains.
If it be further ascertained, that these luminous phenomena are not produced by the inflexion of rays passing over the asperities of the moon's disk, and that they have a real existence, then there will be a new atmosphere to add to those which already surround the sun; for clouds cannot support themselves in empty space.
We come next to that part of the subject which treats of the true place of the sun in the universe. In the year 448 b.c., Archelaüs, the last of the Ionian philosophers, without having made any measurements, taught that the sun was a star, but only somewhat larger than the others. Now, the nearest fixed star is 206,000 times further from us than the sun: 206,000 times 95,000,000 of miles—a sum beyond all our habits of thought. The light from the star Alpha of the Centaur is three years in its passage to the earth, travelling at the rate of 192,000 miles per second; and there are 86,400 seconds in a day, and 365 days in a year. Astounding facts! If the sun, therefore, were removed to the distance of a Centauri, its broad disk, which takes a considerable time in its majestic rising and setting above and below the horizon, would have no sensible dimensions, even in the most powerful telescopes; and its light would not exceed that of stars of the third magnitude—facts which throw the guess of Archelaüs into discredit. If our place in the material universe is thus made to appear very subordinate, we may remember, as M. Arago observes, that man owes the knowledge of it entirely to his own resources, and thereby has raised himself to the most eminent rank in the world of ideas. Indeed, astronomical investigations might not improperly excuse a little vanity on our part.'
Among the stars, Sirius is the brightest; but twenty thousand millions of such stars would be required to transmit to the earth a light equal to that of the sun. And if it were difficult to ascertain the nature and quality of the sun, it would appear to be still more so to determine these points with regard to the stars; for the reason, that the rays, coming from all parts of their disk, at once are intermingled, and of necessity produce white. This difficulty did not exist in similar investigations on the sun, because its disk is so large, that the rays from any one part of it may be examined while the others are excluded. Under these circumstances, further proof might seem to be hopeless; but advantage was taken of the fact, that there are certain stars which are sometimes light, sometimes dark, either from having a movement of rotation on their own axis, or because they are occasionally eclipsed by a non-luminous satellite revolving around them. It is clear, that while the light is waxing or waning, it comes from a part only of the star's disk; consequently, the neutralisation of rays, which takes place when they depart from the whole surface at once, cannot then occur; and from the observations on the portion of light thus transmitted, and which is found to remain white under all its phases, we are entitled to conclude, in M. Arago's words, that 'our sun is a star, and that its physical constitution is identical with that of the millions of stars strewn in the firmament.'
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