by rose colored prominences, compared by some of them to alpine peaks illuminated by the setting sun. In the eclipse of 1851 many of these were drawn, and showed sufficient resemblance to prove them real objects. Not only huge elevations, but lower sierra ridges, widely stretched round the disc. One great prominence was so brilliant as to be visible for five seconds after the end of total eclipse. Mr. Hind speaks of a long range of rose colored flames, seemingly affected by a tremulous motion, their brilliant, rosered tops fading away along the moon's limb into what appeared a bright narrow line of deep violet tint.*

In the total eclipse of 1860, the attention of astronomers was specially directed to this interesting feature. A new feature was here introduced, photographs being successfully taken by Father Secchi and Mr. De la Rue. In these the prominences were plainly shown. The observations of the former induced him to form the following conclusions.

He considered the prominences as real solar appendages, being collections of very brilliant luminous matter, having strong photographic activity. Many were photographed that could not be seen, their rays, perhaps, being all actinic. A zone of the same material as the prominences enveloped the whole sun, from whose surface these flame-like masses sprang.† Some of the latter were of immense height, reaching up to 80,000 miles above the surface, and if their bases lay below the visible edge some of them may have been 130,000 miles high.

During the great eclipse of August 18th, 1868, a more powerful instrument of research was applied. The powers of the spectroscope were now well known and largely developed, instruments of great excellence being in use. Some very good photographs were taken, but the spectroscopic results were the most interesting. Lieutenant Herschel describes, in lively terms, his excitement in turning this new instrument of re

*La plupart des savants les regarderent comme des flammes, ou comme d-es nuages. Le Soleil, p. 179.

+ Compte's Rend. July, 1860.

search upon the mysterious prominences, particularly when three vivid lines met his anxious gaze; red, orange, and blue.

The appearance of these lines was indeed highly significant. It may be well to give a hasty description of the character of spectroscopic observation to render the meaning of these results more clear to those readers who are unacquainted with its principle of action. It has long been known that the colored spectrum, into which the sun's light is extended by the prism, is crossed by numerous dark lines, visible when the spectrum is lengthened and narrowed.

Further experiment proved that a solid or liquid incandescent body gave a continuous spectrum, and that an incandescent gas gave a spectrum of bright lines separated by dark spaces; while the light of a solid body, if passed through a gas, gave a spectrum crossed by dark lines in the exact positions occupied by the bright lines of this gas when incandescent.

The necessary conclusion was soon reached. Each gas had the power of giving out special lines of its own, and of absorbing these same lines from the light emitted by another body. Instruments formed on this principle thus gave observers the power to declare whether a light-giving substance was a gas, or in the solid or liquid state; and, if the latter, whether its light passed through gases in a cooler condition; and finally enabled them to name these gases if similar to any of our earthly elements. It was by this means that the elementary constituents of the sun, as already given, were discovered.

The bright lines, then, of the prominence at once disproved several ideas of their constitution. Had they been self-luminous solar mountains, a continuous spectrum would have appeared. Had they been bodies reflecting solar light, their spectrum would have been crossed by dark lines. The sole remaining theory was that they consisted of glowing, gaseous matter.*

What was this gas? This was the next object of discovery. The three lines seen by Herschel were increased by other ob

* The Sun, p. 279.

*

servers to five, six, and nine lines respectively. We will not give their ideas relative to these lines, as we possess more reliable later information. Mr. Jansen was struck by the brilliancy of some of them, and by the general splendor of the prominences. As he looked, the idea occurred to him that these lines might possibly be seen when the sun was not eclipsed. In this idea lay the germ of the remarkable progress since made in solar astronomy. The next day he applied it successfully to the sun. "I have experienced," he said, "to-day, a continuous eclipse."+

Mr. Lockyer, in England, had meanwhile been studying the edge of the sun with the hope of attaining a similar result. He was incited to this by Dr. Huggins, whose examination of a star that suddenly appeared, in May, 1866, enabled him to declare that its light was due to an outburst of glowing hydrogen, along with which was plainly visible the native spectrum of the star. This rendered it possible that the definite bright lines of a gas might be made visible even through an intenser under-light, and gave Lockyer his cue to disperse the diffused atmospheric light of the sun, and thus give a special advantage to the unchanged lines of the prominences. The effect of such dispersion on these lines is simply to separate them from each other, while the spectrum of the daylight is rendered so faint as not to interfere with their observation.

It needed then but the possession of a sufficiently delicate spectroscope to realize this important idea. This he succeeded in obtaining, and his account of the success of his experiment was read before the French Academy just five minutes before the reception of Mr. Jansen's account of his having made the same discovery.

This new method of observation gave astronomers an unexpected opportunity of observing at their leisure phenomena which they had heretofore only been able to perceive during the fleeting moments of an eclipse. The research has since

*He writes: "Immédiatement après la totalité, deux magnifiques protubérances ont apparu; l'une d'elles, de plus de trois minutes de hauteur, brillait d'une splendeur qu'il est difficile d'imaginer."

The Sun, p. 280. * American Journal of Science and Art, Jan. '69.

VOL. XXVII.-NO. LIII.

6

been diligently prosecuted, with a rapid improvement in modes of observation, and constantly increasing information. These new modes have given astronomers the power of seeing the prominences displayed in their full shape and size, and of observing their every transformation; while their connection with the solar spectrum enabled them to settle positively the true position of the bright lines.

It has thus been satisfactorily proven that the red and blue lines correspond exactly with the C and F lines of hydrogen. Hydrogen, at a glowing heat, was thus shown to be one constituent of these huge vaporous masses. Mr. Lockyer was soon able to confirm the views of those who held that the sun is wholly surrounded by a layer of matter similar to the prominences. This he named the chromosphere. It is doubtful if this be a true solar atmosphere. Its uneven limit resembles rather a region of flames or clouds. It is gaseous, but so are the prominences. Proctor thinks it a gaseous matter suspended in the true solar atmosphere, driven upward by some vigorous power, expanding in the then upper atmosphere, and slowly sinking towards the surface.

It is within the chromosphere and certain prominences that spectroscopes of high dispersive power exhibit remarkable evidences of cyclonic movements taking place in the solar atmosphere. Professor Young has observed the F line of hydrogen greatly displaced, while the C remained unchanged, a fact which shows that we are as yet far from a solution of all the mysteries of the surface condition of the

sun.

Dr. Zöllner has systematically applied Dr. Huggins' method of observing the full shape of the prominence (already adverted to) with interesting results. He saw the prominences in three distinct colors, corresponding to the three lines of their spectrum. The red and blue images did not agree with the yellow, and the latter was only intense near the sun's edge. He supposes it to come from a gas of greater specific gravity than hydrogen, and, therefore, occupying a lower level. He published figures of these prominences, some resembling clouds, others eruptive in form. Some of the latter

seem to be hurled in a vertical line to a great height, then to widen at the top and sink slowly downward.*

Professor Respighi has been yet more systematic, taking daily views round the sun's limb. He considers the prominences solely eruptive, and usually connected, but not identical, with the faculæ. Only low jets appear over the spots, and near the equator and poles they are few and small. He noticed one that appeared to rise to a height of 160,000 miles, Their formation begins with a rectilinear jet, bright and well defined. This rises to a great height, falls over like the jet of a fountain, and slowly sinks, often spreading out like the head of a vast tree.

He gives the following theoretical conclusions from his observations. He considers the photosphere as the surface of an incandescent liquid mass, by whose weight various gases, especially hydrogen, are confined in the interior of the sun at an elevated temperature and under a tension that reduces their density nearly to that of the confining liquid stratum. These gases are not in stable equilibrium, and might thus be pressed upward with great force, bursting through the surface and rising with a velocity depending on the depth from which they come, spreading, from their enormously expansive condition, into vast clouds, and then slowly falling into the chromosphere.+

Thus, there have been successively discovered in the sun, its photosphere, a brilliant surface, marked by the "willow leaves," "rice grains," and "pores" of different writers; its faculæ, ridge-like bodies of peculiar brightness; its spots, dark, cyclonic depressions in the surface; its chromosphere, a layer of luminous gases several thousand miles in thickness; and its prominences, apparently mighty outbursts of glowing gas, incessantly occurring and extending upward to a great height, from which they slowly fall back, like a dense smoke shot vertically upwards, and descending in widely spreading masses through the air.

Still beyond these lies another phenomenon, of equal in

* Jour. Science and Art, Sept. 1869. † Amer. Jour. of Science, Feb. 1871.