The veiled spots have no umbra or penumbra, although they are usually accompanied by faculæ resembling those seen near the ordinary spots. They are frequently seen in the polar regions, but are there always of small size and of short duration. The veiled spots are larger, and more apt to arrange themselves into groups, in the regions occupied by the ordinary spots, and it is not rare to observe such spots transform themselves into ordinary spots, and vice versa. The veiled spots, therefore, seem to be ordinary spots filled up, or covered over by the granulations and semi-transparent gases composing the chromospheric layer. That it is so, becomes more evident, from the fact that large Sun-spots in process of diminution are sometimes gradually covered with faint and scattered granules which descend in long, narrow filaments, and become less and less distinguishable as they attain greater depth. This phenomenon, associated with the fact that the luminous bridges seen over the Sun-spots which are closing up are sometimes transformed into branches which show the characteristic structure of the photosphere, goes far to prove that the solar envelopes are mainly composed of an innumerable quantity of radial filaments of varying height.
PLATE I.—GROUP OF SUN-SPOTS AND VEILED SPOTS.
Observed on June 17th 1875 at 7 h. 30 m. A.M.
The group of Sun-spots represented in Plate I., was observed and drawn on June 17th, 1875, at 7h. 30m. A. M. The first traces of this group were seen on June 15th, at noon, and consisted of three small black dots disseminated among the granulations. At that time, no disturbance of the surface was noticeable, and no faculæ were seen in the vicinity of these spots. On June 16th, at 8 o'clock A. M., the three small spots had become considerably enlarged, and, as usual, the group consisted of two principal spots. Between these two spots all was in motion: the granulations, stretched into long, wavy, parallel lines, had somewhat the appearance of a liquid in rapid motion. At 1 o'clock, P. M., on the same day, the group had considerably enlarged; the faculæ, the granulations, and the penumbral filaments being interwoven in an indescribable manner. On the morning of the 17th, these spots had assumed the complicated form and development represented in the drawing; while at the same time two conspicuous veiled spots were seen on the left hand, at some distance above the group.
Some luminous bridges are visible upon the left hand spot, traversing the penumbra and umbra of this spot in various directions. The umbra of one of the spots is occupied, and partly filled with gray and rosy veils, similar to those above described, and the granulations of the solar surface form a background to the group of spots.
This group of spots was not so remarkable for its size as for its complicated structure. The diameter of the group from east to west was only 2½ minutes of arc, or about 67,000 miles. The upper part of the umbra of the spot situated on the right hand side of the group was nearly 7,000 miles in diameter, or less by 1,000 miles than the diameter of the Earth. Some of the long filaments composing that part of the penumbra, situated on the left hand side of the same spot, were 17,000 miles in length. One of these fiery elements would be sufficient to encircle two-thirds of the circumference of the Earth.
[SOLAR PROTUBERANCES]
PLATE II
The chromosphere forming the outlying envelope of the Sun, is subject, as has been shown above, to great disturbances in certain regions, causing considerable upheavals of its surface and violent outbursts of its gases. From these upheavals and outbursts of the chromosphere result certain curious and very interesting forms, which are known under the name of "Solar Protuberances," "Prominences," or "Flames."