We smile at conclusions which our present knowledge condemns as extravagant and impossible, but such incidental flights of fancy in no way derogate from the high value of Herschel's contributions to solar science. The cloud-like character which he attributed to the radiant shell of the sun (first named by Schröter the "photosphere") is borne out by all recent investigations; he observed its mottled or corrugated aspect, resembling, as he described it, the roughness on the rind of an orange; showed that "faculæ" are elevations or heaped-up ridges of the disturbed photospheric matter; and threw out the idea that spots may ensue from an excess of the ordinary luminous emissions. A certain "empyreal" gas was, he supposed (very much as Wilson had done), generated in the body of the sun, and rising everywhere by reason of its lightness, made for itself, when in moderate quantities, small openings or "pores,"[141] abundantly visible as dark points on the solar disc. But should an uncommon quantity be formed, "it will," he maintained, "burst through the planetary[142] regions of clouds, and thus will produce great openings; then, spreading itself above them, it will occasion large shallows (penumbræ), and mixing afterwards gradually with other superior gases, it will promote the increase, and assist in the maintenance, of the general luminous phenomena."[143] This partial anticipation of the modern view that the solar radiations are maintained by some process of circulation within the solar mass, was reached by Herschel through prolonged study of the phenomena in question. The novel and important idea contained in it, however, it was at that time premature to attempt to develop. But though many of the subtler suggestions of Herschel's genius passed unnoticed by his contemporaries, the main result of his solar researches was an unmistakable one. It was nothing less than the definitive introduction into astronomy of the paradoxical conception of the central fire and hearth of our system as a cold, dark, terrestrial mass, wrapt in a mantle of innocuous radiance--an earth, so to speak, within--a sun without.