The background shows the sun's visible surface, or _photosphere_, as seen with a telescope of high power at the most favorable moments, composed of innumerable light markings, or granules, separated by a network of darker gray. The granules, each some hundreds of miles in width, are thought to be the flame-like summits of the radial filaments or columns of gas and vapor which compose the photospheric shell. The two principal sun-spots of the group here represented show the characteristic dark _umbra_ in the centre, overhung by the thatch-like _penumbra_, composed of whitish gray filaments. The penumbral filaments are not supposed to differ in their nature from those constituting the ordinary photosphere, save that they are seen here elongated and violently disturbed by the force of gaseous currents. Both spots are traversed partly or wholly by bright overlying _faculæ_, or so-called _luminous bridges_, depressed portions of which, in the left-hand spot, form the _gray and rosy veils_ commonly attendant upon this class of spots. In each of these spots, also, the inner ends of projecting penumbral filaments have fallen so far within the umbra as to appear much darker than the rest. At the right of the upper portion of the left-hand spot, is a mass of white facular clouds, honey-combed by dark spaces, through which are seen traces of the undeveloped third spot of the triple group first observed. If seen upon the sun's limb, this would have presented the appearance of a _lateral spot_. Above the right-hand spot is a small black "dot," or incipient spot, without distinct penumbra. The irregular dark rift below the two large spots and connecting them is a spot of the crevasse type, with very slight umbra, a still better example of which is seen in a westward prolongation of the penumbra of the left-hand spot. In the upper left-hand corner of the Plate are seen several small _faculæ_, appearing as irregular whitish streaks amongst the granules. In the pear-shaped darkening of the solar surface below and at their left, is seen a veiled spot, two of which attended this group. _Approximate scale, 2500 miles--1 inch._ PLATE II.--SOLAR PROTUBERANCES. _Observed May_ 5, 1873, _at 9h. 40m. A. M._ A view of an upheaval of the _chromosphere_, or third outlying envelope of the sun, as observed with the tele-spectroscope, or telescope with spectroscope attached.