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These particles are most likely driven up from the sun by some electrical action, and are constantly in motion, much as are the streamers of the aurora. Below the corona and sharply separated from it the observer finds another body of very dense vapour, which is termed the chromosphere, and which has been regarded as the atmosphere of the sun. This layer is probably several thousand miles thick.
Below the chromosphere is the photosphere, the lower envelope of the sun, if it be not indeed the body of the sphere itself; from this comes the light and heat of the mass. This, too, can not well be a firm-set mass, for the reason that the spots appear to form in and move over it.
Frankland and Lockyer communicated to the Royal Society a series of experiments on gaseous spectra under varying conditions of heat and density, leading them to the conclusion that the higher solar prominences exist in a medium of excessive tenuity, and that even at the base of the chromosphere the pressure is far below that at the earth's surface.
Certain of the included species mimic terrestrial cloud-scenery now appearing like fleecy cirrus transpenetrated with the red glow of sunset now like prodigious masses of cumulo-stratus hanging heavily above the horizon. The solar clouds, however, have the peculiarity of possessing stems. Slender columns can ordinarily be seen to connect the surface of the chromosphere with its outlying portions.
[Footnote 26: I should add that while M. Faye ascribes solar spots to clouds formed within cyclones, we differ concerning the nature of the cloud. I have argued that it is formed by rarefaction, and consequent refrigeration, of the metallic gases constituting the stratum in which the cyclone exists. He argues that it is formed within the mass of cooled hydrogen drawn from the chromosphere into the vortex of the cyclone. Speaking of the cyclones he says: "Dans leur embouchure évasée ils entraîneront l'hydrogène froid de la chromosphère, produisant partout sur leur trajet vertical un abaissement notable de température et une obscurité relative, due
In September, 1871, Young drew up at Dartmouth College a list of 103 lines significant of injections into the chromosphere of iron, titanium, chromium, magnesium, and many other substances.
From the manner in which it moves, in the way the air of our own planet does in great storms, it is not easy to believe that it is a fluid, yet its sharply defined upper surface leads us to suppose that it can not well be a mere mass of vapour. The spectroscope shows us that this chromosphere contains in the state of vapour a number of metallic substances, such as iron and magnesium.
It floated tranquilly above the chromosphere at an elevation of some 15,000 miles, and was connected with it by three or four upright columns, presenting the not uncommon aspect compared by Lockyer to that of a grove of banyans. Called away for a few minutes at 12.30, on returning at 12.55 the observer found
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