forms the sun. What is it? The earliest observers who studied the appearance saw it to be a shining sphere, and to this day no one has been able to say with certainty much more than that it is a hot shining sphere. No doubt a modern might be able to say a little more than this to an ancient, but would his information be in the direction of telling him what the photosphere is? Let us see: The first and simplest thing we should expect to know about it is whether it is solid, liquid, or gaseous; but this very first question is one which no one has been able to answer with certainty, and respecting which the greatest diversity of opinion prevails. Some hold it to be solid, admitting of course that it must be frequently melted or broken up in places by the intense heat rising from the interior, but maintaining a general solid texture. Others consider it as a mixture of gaseous and solid matter or of solid and liquid matter, while still others regard it as purely gaseous. And none of these conflicting views can be either supported or overthrown by unanswerable arguments.

If so little is known of that part of the sun which all mankind have seen whenever they looked at it, what shall we say of the more obscure features which have only been discovered in recent times?

We have alluded to the extraordinary activity which prevails at the surface of the sun, and which is shown by its belching forth immense volumes of hydrogen gas and vaporized metals to heights of fifty or one hundred thousand miles, or by its projecting them along its surface with velocities of one hundred. or two hundred miles a second.

If this takes place at the surface, what, we would ask, must be the agitation in the interior? Yet immediately beneath all this inconceivable activity we have a photosphere seemingly so calm that the most refined observation has hardly been able to show any deviation from a perfectly spherical outline. True, it is from time to time subject to change, especially by a formation and closing up of spots; but these changes are nothing compared with the agitation of the chromosphere which immediately surrounds it. It seems to the writer that in this contrast between the serenity of the photosphere and the agitation of the chromosphere or layer of gaseous metals which immediately

surround it we must have a key to a theory of solar activity. Yet he is hardly aware of a serious attempt to make use of the

key for this purpose.

Let us return again to the corona. We know that gravitation at the surface of the sun is about twenty-seven times as intense as at the surface of the earth. All the matter which surrounds the sun should therefore fall to its surface, as at the surface of the earth, unless sustained by some opposing forces; but what prevents this corona matter from so falling? That it cannot be an atmosphere sustained by its own elasticity, and resting on the surface of the sun, seems to be abundantly proved. We may suppose it held up by electric repulsion, but this is purely a guess, without the slightest foundation in observation. All we can say with certainty on this subject is that we know nothing about it.

Perhaps the difficulty we meet with may be made more clear by considering one of the features of the solar spots. The earlier observers found these spots to comprise a dark central portion which they called the umbra, surrounded by a shaded border, sometimes nearly as bright as the sun itself, which they called the penumbra. When this border was studied with the best telescopes and in good atmospheric conditions, it was found to exhibit a very singular structure. Instead of being of nearly uniform tint, or slightly mottled like the surface of the sun, in general it was found to have a fibrous appearance, like the threaded fringe of a shawl or of the end of a straw-thatched roof. The threads were at right angles to the edge of the spot; that is, they projected from the bright photosphere surrounding the spot towards the centre of the latter. Here we have a very interesting phenomenon of the spots, and one which has often been depicted. But what are these fibres? And what is their relation either to the photosphere or to the spot? To this question, and to all others connected with the subject, we have to answer with our silence. It seems to be pretty well established that the solar spots are openings in the photosphere. This being the case, we might imagine the thatch-work to form the framework of the photosphere itself, and when the photospheric or brilliant matter is removed in order to form the spot, a portion of this framework to remain around the edges

of the opening-much the same as when a hole is dug in a mixture of soft earth and straw, the ends of the straw will project from all sides into the hole. But it would, be wholly unwarranted to assume any such connection between the photosphere and the thatch-work. We have not the slightest evidence that the latter extends into the photosphere to form its framework. Therefore, as in all the other cases we have considered, all we can say is that we know nothing about it.

That man will not be satisfied to rest in this state of ignorance, we may be assured. The sun as the supporter of all life and movement on the surface of our globe must be regarded as the most important object of investigation with which science has ever concerned itself. No disappointment will, therefore, damp the ardor of those who are engaged in researches upon it. We may reasonably hope that the near future shall be more glorious than the past, and that if a satisfactory theory of the sun's constitution is not formed we shall still be able to reach some conclusion respecting the sources, the duration, and the possible changes of its supply of heat.

SIMON NEWCOMB.

N

THE RECENT SOLAR ECLIPSE.

O natural phenomenon is more impressive than a total eclipse of the sun, and very few possess a higher scientific

interest.

The aspect of the earth in the strange light of the solar crescent, the onrushing shadow, the sudden swoop of the darkness, the lighting up of the stars, the serene radiance of the coronal shining calmly around the dark globe which has supplanted in the sky the orb of day, and the victorious outburst of the sunlight at the end-these all combine to produce a series of sensations and emotions to be obtained in no other way, and never to be forgotten.

The rarity of the phenomenon adds to its interest, since very few can ever have the opportunity of seeing it more than once, or even at all, except by making special journeys for the purpose. At London, for instance, there was no total eclipse of the sun in all the interval between 1140 A.D. and 1715, according to Halley; and Hind has shown that even the eclipse of 1715 was not quite total there, that there has not been one there since, and that there will not be one during the whole of the coming century, though in 1999 the moon's shadow will pass very near the city.

London has been, perhaps, rather unusually unfortunate in this respect, but it is far within bounds to say that at any given place total eclipses of the sun do not occur as often, on the average, as once in a century. Of course the explanation of this extreme rarity of total eclipses at any particular place is not that they happen so seldom, but that, when they do occur, they are visible as total only over a limited area. The shadow

of the moon, as it traverses the earth, can never be more than 160 miles in width, and is usually much narrower.

If, however, we consider the whole surface of the earth, total solar eclipses are not at all uncommon, happening, on the average, as often as once in two years. The Chaldeans long ago discovered that eclipses recur approximately in a regular cycle of a little more than 18 years, and gave to this cycle the name of Saros. In this period there are usually about 70 eclipses 29 of the moon and 41 of the sun; and of the solar eclipses about one fourth are total, the rest being annular or simply partial.

The astronomical interest of eclipses is twofold. They furnish, on the one hand, exceedingly accurate determinations of the moon's place with reference to the sun, from which are derived data of the highest importance in the lunar theory. In the other, they present an opportunity, short but precious, for studying the solar atmosphere, and the strange envelope of luminous matter at other times hopelessly concealed by dazzling sunlight. Then, also, we can search the sky in the neighborhood of the sun for new and unknown, though not unsuspected, planets circulating in orbits of smaller diameter than that of Mercury.

All eclipses, therefore, are carefully observed, and from their observation results have been deduced of the highest scientific importance.

It will be proper here, as an introduction to our account of the late eclipse, to present some brief notice of the more remarkable eclipses which have occurred in recent years, in order that we may have a clearer view of the nature of the problems involved and the progress made toward their solu tion.

In 1842, on July 8th, just two Saros periods before the eclipse of last July, the moon's shadow traversed Southern France, Northern Italy, and part of Austria. The eclipse was observed with great care by a multitude of astronomers, conspicuous among whom was Arago. On this occasion the polariscope was first applied, and showed the polarization of the light of the corona. The principal result of the eclipse was, however, to concentrate scientific interest upon certain