Page:Collier's New Encyclopedia v. 09.djvu/197

LEFT SXTN 163 SUN different heights in it, different lines, or the same lines with different intensity, will appear, in accordance with his theory that in the sun our chemical ele- ments are dissociated and float at dif- ferent levels in the solar atmosphere. This is one of the points to be settled by observation at future eclipses. Chromosphere and Prominences or Protuberances. — Above the reversing layer and interpenetrating it, or possibly identical with it, if Lockyer's theory should prove true, is an atmosphere of permanent gases called the chromo- sphere. Hydrogen is the most abundant of these gases, and out of this chromo- sphere rise the wonderful prominences or protuberances which form so promi- nent a feature of the sun's surroundings at the time of a total eclipse, and which can be investigated by the spectroscope at any time as they consist almost wholly of hydrogen. They are of all imagin- able fantastic shapes, and frequently rise, and are sometimes seen to be rapid- ly projected to the height of several hun- dred thousand miles, and at enoi'mous velocities. In such case they are almost always seen to be connected with some active sunspot, and they are unquestion- ably the results of the upheavals, erup- tions, or explosions accompanying the surroundings of the spots. The chromo- sphere itself all along the limb of the sun, as seen in the hydrogen lines in the spectrum, is not a smooth, flat layer, but consists of filaments like upward tongues of flames, and has been com- pared to the appearance of a "prairie fire," though there is no actual combus- tion going on. Spectrum and Constitution. — Almost all our knowledge of the constitution of the sun has been revealed to us by the spectroscope. It has shown us that not only do many of our so-called chemical elements exist in the sun, but that its temperature is so high that they exist there in the form of gases. Among the elements identified are hydrogen, iron, titanium, calcium, manganese, nickel, cobalt, chromium, barium, sodium, mag- nesium, and platinum, with a strong probability in favor of copper, palladium, vanadium, molybdenum, uranium, alu- minum, cadmium, carbon, and lead. With the exception of carbon all the above are metals. (Hydrogen in its chemical relations ranks as a metal.) A few years ago it was considered that the late Dr. Henry Draper had shown the strong probability of the existence of oxygen in the sun, but the later investi- gations, while not decisive, tend to nega- tive this conclusion. In this connection Mr. Lockyer's views must be mentioned. He considers that none of our so-called chemical elements are truly elementary, but that they may all be decomposed into simpler constituents, and that many of them are so dissociated in the sun and the stars. The matter is still one of the most important unsettled questions in the domain of astro-physics. A full ex- position of his views may be found in his "Chemistry of the Sun." The revela- tions of the spectroscope in regard to the chromosphere, prominences, and so-called reversing layer have already been briefly mentioned. It has also been instrumen- tal in revealing the enormous velocities accompanying explosions, and eruptions on the sun. At the limb of the sun we see these revealed by the telescope di- rectly in the huge hydrogen prominences, but the spectroscope shows another com- ponent of this velocity in the direction to or from us in the line of sight. In the spectrum of a spot, and of the faculae round it, the lines are frequently broken and twisted into remarkable shapes, in- dicating motion to or from us of the gases in question at enormous velocities. In some cases hydrogen has been shown to be rushing toward us with a velocity of 300 miles per second. Occasionally the spectrum of the nucleus of a spot has shown a down-rush of matter into the cavity. The Solar Corona. — Surrounding all other parts of the solar surface rises the halo of light called the corona, which is only visible at the time of a total eclipse. Though known from the remotest times, little is yet known of its cause or physi- cal condition, and it is the principal ob- ject of attack now at the time of every eclipse of the sun. Down near the sur- face it is very bright and of a pearly or greenish color. Above this it rises, especially at the poles, in short, finely clustered filaments. Over the sunspot zones it generally rises higher in broad streaks, and at times extends out nearly in the direction of the ecliptic in faint streaks looking like gauze wings on the sun. These fade out gradually, and their limit to the eye or the photographic plate is fixed by the brightness of the sky background. Up in the clear air of Pike's Peak, Col., in 1878, these streamers were seen extending at least 9,000,000 miles from the sun. It varies much at differ- ent eclipses and is never twice alike, though certain typical forms seem to fol- low somewhat the maxima and minima of the sunspot period. The total light of the corona is at least two of three times that of the full moon. As its light ap- pears to be relatively rich in the ultra violet part of its spectrum, Dr. Huggins