of a gradual shading off from the surrounding brightness to the dark center, the border is marked with parallel lines, which give it an appearance like that of the lower edge of a thatched roof.

Besides the wonders on the very surface of the Sun, observations made with powerful instruments in the time of total eclipses have discovered new marvels. total obscuration the dark disk of the surrounded with a halo of silvery light.

At the moment of moon is found to be

This halo is some

times seen extending on all sides to the apparent distance of half the diameter of the Sun. What this corona, as it is called, is composed of, no one can tell. It is not an atmosphere in any degree like that of the Earth. A stratum of any kind of

gas, held in place by gravitation, would maintain a uniform height from the surface; whereas the corona presents a very irregular outline.

There are, also, visible during total eclipses appearances which have received various names, "prominences," "flames,"

"protuberances," etc. These sometimes rise to the enormous height of fifty thousand miles above the surface of the Sun.

When astronomers discovered them, the first thought was that they are clouds of some sort, floating upward from the fiery deep, and reflecting its rosy light. The spectroscope shows that this is an error, and that these enormous columns, fantastic and variable in their forms, are masses of hydrogen gas, so hot as to shine by their own light. And nearer the body of the Sun, close above the burning surface, there seems to be a stratum of this same gas, intensely heated, from which shoot up, from time to time, these mighty tongues of flame. This is called the chromosphere. The spectroscope reveals another fact. While it shows that hydrogen, iron, and some other substances well known to us, enter into the composition of the Sun, there are many lines in the spectrum which are not recognized as belonging to any element of this earthly creation. What they are none can even conjecture.

In short, the sun is the scientific crux philosophorum. To the unaided eye it seemed calm, silent, powerful, shining upon the worlds in its stillness and strength. Viewed through the lenses of the astronomer, it is an ocean of flame, swept by currents compared with which our Gulf-stream is only a ripple in a summer brook, and tossing perpetually with wilder tempests than earthly oceans feel when wrecked navies strew the shore. From time to time, here and there, from the hot deep there open wide mouths, as of volcanoes, into which a world like this might fall, and from them issue masses of flame that leap upward thousands of miles, and throw their light to the stars. What fuel feeds this fiery furnace; what power within bursts forth in these floods of light and heat; what winds sweep these seas of flame, no mortal can tell. Science can only watch from afar the rush and rage of the storm, and realize the narrow limits of human knowledge.

Is it possible to present in language any adequate idea of the scale on which natural operations are here carried on? If we call the chromosphere an ocean of fire, we must remember that it is an ocean hotter than the fiercest furnace, and as deep as the Atlantic is broad. If we call its movements hurricanes, we must remember that our hurricanes blow only about a hundred miles an hour, while those of the chromosphere blow as far in a single second. They are such hurricanes as, "coming down upon us from the

north, would, in thirty seconds after they had crossed the St. Lawrence, be in the Gulf of Mexico, carrying with them the whole surface of the continent in a mass, not simply of ruin, but of glowing vapor, in which the vapors arising from the dissolution of the materials composing the cities of Boston, New York, and Chicago, would be mixed in a single, indistinguishable cloud." When we speak of eruptions, we call to mind Vesuvius burying the surrounding cities in lava; but the solar eruptions, thrown fifty thousand miles high, would ingulf the whole earth, and dissolve every organized being on its surface in a moment. When the media

val poets sung

Dies ira, dies illa
Solvet sæclum in favilla,

they gave rein to their wildest imagination, without reaching any conception of the magnitude or fierceness of the flames around the sun.-P. 262.

With this eloquent passage from the author we leave the vast problem. What science may hereafter achieve we know not; nor is it safe to say at what point its victories must cease. We can only say that in the present state of science the solar mysteries are not solved. Professor Newcomb gives the views of four distinguished students of the Sun, Rev. Father Secchi, of Rome; M. Faye, of Paris; Professor Young, of Dartmouth College; and Professor Langley, of Allegheny Observatory; to which the still later theory of Dr. Henry Draper, of New York, is appended, stating his discovery of glowing oxygen in the Sun, by means of the spectroscope. These theories differ one from another in some degree, and from some of the views expressed by our author; but these differences only reveal more clearly the magnitude of the difficulty. The spirit of all these able men is well expressed in a single sentence of the closing paragraph of Professor Young's paper: "Such, in brief, are my opinions; but many of them I hold with little confidence and tenacity, and anxiously await more light." This modesty distinguishes the true scientist from the pretender. A quack knows every thing.

THE PLANETS.-As has been already stated, investigation has found an error in the former measurements of the Solar System, and we are compelled to reduce the figures all along the line. These later investigations have detected some other errors, and made important discoveries, and achieved great advances; and yet, as regards the sum of what we think we

know, it is a question whether the new facts added, or the old supposed facts to be thrown overboard, are the more numerous. Mercury was formerly supposed to give indications of an atmosphere. At the beginning of the century Schröter thought he saw mountains twelve miles high on this planet; and, by watching them from night to night, figured out the time of Mercury's daily revolution, computing it to be twenty-four hours and five minutes. More modern astronomers, with better instruments, have not found these lofty mountains, nor seen signs of an atmosphere; nor do they know certainly the length of its day. From time to time, for the last hundred years, publication has been made of the discovery of one or more planets revolving in orbits between Mercury and the Sun. The best observers of the present day have not discovered them, and we can only conclude, at present, that there are

none.

Venus has long been supposed to be surrounded by an atmosphere; and the observations of 1874 are held to establish the fact. Some other suppositions of the past have not stood the test. Schröter thought that he proved the existence of mountains twenty miles high on the surface of this planet, and, watching them from day to day, concluded that Venus revolves. on its own axis in twenty-three hours and twenty-one minutes. Astronomers of our own day, aided by better instruments, fail to discover these lofty mountains; nor can they fix on any thing by which the time of rotation may be ascertained.

Cassini, two hundred years ago, fancied that he saw a satellite of Venus. During the next century several observers imagined that they, also, saw it; and one astronomer proceeded to compute its orbit. It cannot be found now, and seems to have been nothing but a myth at any time. About the only real addition recently made to our knowledge of this body is the fact, shown by the spectroscope, that its atmosphere is composed of materials similar to the atmosphere of our Earth. If this is so, the supposition is not an extravagant one, that Venus is a world much like our own, perhaps peopled by similar living beings.

In regard to the Earth, the principal new fact is the one already given, the conclusion that the distance from the Sun is not as great, by three millions of miles, as former figures stated

it. The results of the observations of 1874 will soon be at hand, to confirm or modify this estimate. On a certain question, which is geological rather than astronomical, and yet bears directly on the theory of the formation of the Solar System, Professor Newcomb is quite explicit. He accepts the theory that the interior of the earth is intensely hot, perhaps molten.

It is well known that as we descend into the solid portions of the Earth there is a uniform rise in the temperature, equal to one degree of Fahrenheit for every fifty feet, or one hundred degrees to the mile. The author says that "we have every reason to believe" that this increase "continues many miles into the interior. Then we shall have a red heat at the distance of twelve miles; while at the depth of one hundred miles the temperature will be so high as to melt most of the materials which form the solid crust of the globe. "-Pp. 299. Hot springs, volcanoes, and earthquakes give strong evidence to sustain this view. Still, there is evidence adverse to the idea of a wholly molten interior. If the entire globe, with the exception of a crust fifty or a hundred miles in thickness, were liquid, the tides would effect the whole mass, and not the oceans only. The solid crust would rise and fall, the land as well as the sea, and no tides be seen along the shore.

In discussing things pertaining to the Earth, the author treats of the Aurora Borealis. The number of comparatively new facts in regard to it is not large, yet they are interesting. Observations made at the same time from distant points show that the visible phenomena take place from four hundred to six hundred miles above the surface of the Earth. They are rarely seen near the Earth's equator, but are most frequent, not at the extreme north, but in the region of the Arctic circle. It may be regarded as certain that the Aurora is electric in its nature, and is closely connected with terrene magnetism. The auroral light has been examined with the spectroscope, and is found to exhibit some new lines, which wait, and may wait long, for explanation.

To our knowledge of the Moon modern researches seem to have added little. There is no evidence of the existence of an atmosphere, no indications of change of any kind upon its surface. We are indebted to it for its silvery light; it heaves the