New Manuel
of the
Elements of Astronomy
by
Henry Kiddle, A. M.
1867
of the
Elements of Astronomy
by
Henry Kiddle, A. M.
1867
155. Theories as to the Physical Constitution of the Sun -- The most generally received hypothesis as to the nature of the sun is that it is an opaque body surrounded by an atmosphere of luminous matter, and that the spots are openings in the atmosphere, through which the dark body of the sun becomes visible.
a. This hypothesis was first advanced by Dr. Wilson of Glasgow, in 1769. In 1793 Sir William Herschel suggested the hypothesis that two atmospheres encompass the sun; the first for lower one being formed of a partially opaque or cloudy stratum reflecting light, but emitting none of itself; and the second consisting of luminous matter, which is the source of the sun's light, and gives to the disc its form and limit. This luminous atmosphere has been sometimes called the photosphere.
b. The existence of a third atmosphere, very nearly transparent, and extending a great distance above the photosphere, is clearly indicated by the diminished brightness of the sun's disc toward the edges.
c. Wilson's and Herschel's hypotheses, as developed and modified by more recent observations,explain all the phenomena of the spots. The black umbra is the body of the sun, while the penumbra is the non-luminous atmosphere, or cloudy stratum, rendered visible by the larger opening in the atmosphere above it. When this opening is smaller, no penumbra is visible; and when there is no opening in the cloudy stratum, no black nucleus is visible. These openings or rents are supposed by Sir John Herschel to be caused by changes of temperature, in a manner similar to the production of tornadoes and other agitations of the earth's atmosphere.
156. The spots and other appearances on the sun's disc indicate, without doubt, the existence of a luminous atmosphere, consisting of gaseous matter in an incandescent state, -- like the flame of an ordinary gas-burner, -- and another atmosphere, also gaseous, and almost perfectly transparent, extending to a considerable distance beyond.
a. The Gaseous character of the atmosphere, denied by Sir William Herschel, seems to have been conclusively proved by M. Arago, by means of an ingenious application of the principle of polarized light. M. Faye estimates the height or extent of the photosphere at 4, 000 miles.
b. Kirchhoff's Hypothesis -- A simpler hypothesis than Wilson's and Herschel's has within the last five years been advanced by Kirchhuff, a German physicist, and others, to account for the phenomena of the spots, consistently with the established facts, as above stated. According to this hypothesis the nucleus of the sun is an incandescent, solid or liquid mass, the vapors arising from which form the atmosphere, the denser and lower one being luminous from the incandescent particles that float in it. Changes of temperature in this atmosphere give the rise to tornadoes and other violent agitations; and descending currents produce the openings, which are dark because filled with clouds of various degrees of condensation. This theory, and the experiments upon which it is based, are receiving, at present, much attention from astronomers and physicists; and there is reason to believe, that when fully developed, it will entirely supersede the cumbrous and therefore improbable hypothesis so long and so ingeniously sustained.
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