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.