The figure and the text below are from “A popular handbook and atlas of astronomy” by Sir William Peck (1862-1925), published in New York in 1891.
That portion of the sun from which we receive our light — the visible surface, or the photosphere— is simply a shell of glowing vapour about 10,000 miles in thickness. Below this region there is the gigantic central ball of the sun, 850,000 miles in diameter, about which astronomers know httle or nothing, beyond the fact that it cannot be solid. From the intensity of the internal heat, it is known that even the centre of the sun or the densest part of the solar globe, notwithstanding the enormous pressure to which the particles composing it are subject, consists of some gaseous material, though the vapour there is doubtless, from the pressure, as heavy as the densest of our metals.
Lying immediately above the photosphere, and extending outwards to an unknown distance, is the sun’s so-called atmosphere. This atmosphere, completely surrounding the solar globe, is in nature exceedingly complex. Its base, extending from the visible surface for about one thousand miles, is chiefly composed of the heavier metallic vapours, such as the vapour of iron, copper, zinc, & c. Above this layer the uncondensed gases are much lighter, and consist principally of hydrogen. This part extends upwards to about 10,000 miles, and from its coloured appearance is called the chromosphere. In it the most wonderful changes arc ever taking place. Eruptions are constantly projecting monster jets of hydrogen gas, mixed with metallic vapour, to great heights, sometimes to over 100,000 miles. Generally these prominences, as they are designated, are of a blood-red colour, and can only be seen either by aid of the spectroscope, or during a total solar eclipse.
