FIRST ECLIPSE RESULTS.
OUR anticipations respecting the results of the observations to be made during the Total Eclipse of July 29 last have been fulfilled with somewhat singular exactness, considering how small was the antecedent probability that a correct guess, or rather a correct series of guesses, would be made. We said that probably the most interesting result of the study of the sun during the eclipse would be the determination of some difference in character between the corona as seen at a time when the sun is greatly dis- turbed, and at a time like the present, when no spots, or very few, are seen for weeks together. From every region where the eclipse was observed comes the news that the corona on this occasion was utterly unlike the corona in 1871. According to Mr. Lockyer, who observed both eclipses, the corona was greatly reduced in size, but ten times as bright as in 1871. From other observers we have actual measurements of the corona, whose height was estimated at 70,000 miles only, considerably less than the height of several of the loftier prominences seen in 1870 and 1871. On those occasions the inner corona reached certainly to a height of 200,000 miles from the sun, while some of the radiations were measured and photographed as extending to nearly a million miles from the sun's surface. Again, the corona last month differed remarkably in structure and constitution from the corona in 1872. Instead of presenting most complex details of structure, thousands of interlacing filaments, and strangely curved streamers, the corona showed indications of definite structure in two regions only. In 1871 a large part of the corona's light came from gaseous matter ; this matter was of two kinds. First, there was some substance unknown, shining with monochromatic green light, corresponding in position to a part of the spectrum which in Kirchhoff's scale is numbered 1471; secondly, there was glowing hydrogen. IV hen Respighi and Lockyer, using a method suggested by Professor Young in 1870, observed the corona through a battery of prisms (not using any slit), they saw on the continuous rainbow-tinted background produced by multiplied images of the corona, three distinct bright images of the interior part of the corona to a height of some 200,000 miles from the sun's surface. The brightest of the images was the green one, corresponding to the tint 1471 Kirchhoff; the other two were red and blue, and were formed by rays belonging to hydrogen. It was thus shown that in 1871 the corona consisted of two dis- tinct kinds of matter, each probably including several substances of the same general nature. One part of its light came from glowing gas, and this part was itself duplex, two distinct gases being present ; the other part of its light came from glowing solid or liquid matter, this part coming from comical dust, in which many elements were probably present. Now, during the last eclipse Lockyer and Draper each employed a method which, though not absolutely identical with the method employed by Lockyer and Respighi in 1871, was equivalent to it in principle. But they saw no distinct images of the corona, only a bright, rainbow-tinted spectrum. That there was no mistake in this observation is shown by the fact that other observers who studied the spectrum of the corona in the usual way, examining through a slit a fine strip only of its image, obtained a rainbow-tinted spectrum without bright lines,—the meaning of which is that no gaseous matter glowing with its own light was present in the corona, or at least that if any were present, its lustre was not sufficient to form images which could be separately seen. It certainly was not for want of heat that any gaseous matter present in the corona failed to glow with light of sufficient intensity to form a separate image, for the corona being so greatly diminished in extent, every part of it must have been subjected to a much more intense degree of solar heat. But indeed the intense heat of the corona was shown in two distinct ways. Not only were bright lines wanting from the
spectrum of the corona, but no dark lines were seen. The mean- ing of this is that the light of the corona on this occasion was not (in the main, at any rate,) reflected sunlight; for if it had been, the solar dark lines should have been seen in the corona' spectrum, precisely as they are seen in the spectrum of light from our own sky. Then, again, Professor Edison, by means of an • ingenious instrument of his own devising, called the tasimeter, was actually able to measure the heat received from the corona, and found it to be considerable. It follows then—and this seems to us a most striking and interesting discovery, though by no means an un- expected one—that the light of the corona on this occasion came chiefly from glowing solid or liquid matter. In other words, the particles, not necessarily very minute, forming the corona, were caused, by the intense heat to which they were exposed, to glow with a brilliant light. When we consider that at a distance ipf 70,000 miles from the sun, he would appear as an orb a hundred thousand times larger than the sun we see, and would give a correspondingly increased supply of light and heat, we cannot greatly wonder at this result. But it is strange to think of the existence of millions of millions of bodies, small and great, meteoric probably in their nature, travelling close by the sun, and excited by him to so intense a degree of heat as thus to glow with their own inherent lustre.
Again we expressed the opinion that by carefully arranged naked-eye study of the corona, the extension of its faint outlying portions might be recognised to a far greater distance from the sun than on former occasions. We are glad to learn that Professor Newcomb has made observations by the very plan we had in our thoughts, viz., by carefully screening from the eye before and during totality the light from the region round the dark body of the moon. He had erected a screen on a high pole, and with his eyes thus protected from the bright light of the inner corona, he was able to trace the faint luminosity of its outer part to a distance of about six degrees from the sun. In other words, be recognised the prolongation of the corona into the Zodiacal Light. As six degrees from the sun would correspond to a dis- tance of about ten millions of miles, and hitherto the faintest part of the corona had not been traced further than one million miles or so from the sun, Professor Newcomb's observation fully bears out our anticipation that on this occasion the domain of the corona would be widely extended.
But perhaps to many the most interesting of the observations recorded on this occasion will be that relating to an intra- Mercurial planet. It is announced that Professor Watson, of Ann Arbor, detected a body equal in brightness to a star of between the fourth and fifth magnitudes close by the sun. The position of this body is mentioned in a telegram sent by Watson to the Times, and from the recorded place we find that the body was about 2r from the sun's centre, or 21° from his edge. The place indicated is suspiciously near that of the fifth-magnitude star Theta Cancri, and if it were not for Professor Watson's skill in such matters (he has discovered about a score of planets), we should be disposed to imagine that he had omitted Theta from his chart of stars likely to be visible near the sun during totality. Under the actual circumstances, we must infer that be saw Theta Canoni as well, and perhaps it was by aomparing the unknown star with Theta that he was able so definitely to determine the brightness of the stranger,—otherwise a somewhat difficult task, when we remember how unlike the sky near the eclipsed sun is to the sky on which astronomers are in the habit of seeing the stars. It will be singular if the new body should turn out to be Vulcan itself,—that is, if any of the theories of Vulcan between which Leverrier said that astronomers have to choose, should assign to that planet a position corresponding with that in which Watson observed an unknown star.
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