The chromosphere and prominences might be figuratively described as an ocean and clouds of tranquil incandescence, agitated and intermingled with waterspouts, tornadoes, and geysers of raging fire. Certain kinds of light are at all times emitted by them, showing that certain kinds of matter (as, for instance, hydrogen and “helium”[14]) form invariable constituents of their substance. Of these unfailing lines Professor Young counts eleven.[15] But a vastly greater number appear only occasionally, and, it would seem, capriciously, under the stress of eruptive action from the interior. And precisely this it is which lends them such significance; for of what is going on there, they have doubtless much to tell, were their message only legible by us. It has not as yet proved so; but the characters in which it is written are being earnestly scrutinised and compared, with a view to their eventual decipherment. The prodigious advantages afforded by high altitudes for this kind of work were illustrated by the brilliant results of Professor Young’s observations in the Rocky Mountains during the summer of 1872. By the diligent labor of several years he had, at that time, constructed a list of one hundred and three distinct lines occasionally visible in the spectrum of the chromosphere. In seventy-two days, at Sherman (8,335 feet above the sea), it was extended to 273. Yet the weather was exceptionally cloudy, and the spot (a station on the Union Pacific Railway, in the Territory of Wyoming) not perhaps the best that might have been chosen for an “astronomical reconnaissance.”[16]