The spots, the faculae, the prominences, are all, in different ways, of the nature of storms in an atmosphere; that is to say, that, in the great gaseous bulk of the Sun, certain local differences of constitution, temperature, and pressure are marked by these different phenomena. From this point of view it is most significant that many spots are known to last for more than a month; some have been known to endure for even half a year. The nearest analogy which the Earth supplies to these disturbances may be found in tropical cyclones, but these are relatively of far smaller area, and only last a few days at the utmost, while a hundred miles an hour is the greatest velocity they ever exhibit, and this, fortunately, only under exceptional circumstances. For a wind of such violence mows down buildings and trees as a scythe the blades of grass; and were tornadoes moving at a rate of 300 miles an hour as common upon the Earth as spots are upon the Sun, it would be stripped bare of plants and animals, as well as of men and of all their works. It is not an accident that the Sun, when storm-swept, shows this violence of commotion, but a necessary consequence of its enormous temperature and pressures. As we have seen, the force of gravity at its surface is 27·65 times that at the surface of the Earth, where a body falls 16·1 feet in the first second of time; on the Sun, therefore, a body would fall 445 feet in the first second; and the atmospheric motions generally would be accelerated in the same proportion. The high temperatures, the great pressures, the violent commotions which prevail on the Sun are, therefore, the direct consequence of its enormous mass. The Sun is, then, not merely the type and example of the chief source of light and heat in a given planetary system; it indicates to us that size and mass are the primary tokens by which we may judge the temperature of a world, and the activity to be expected in its changes. CHAPTER IV THE DISTRIBUTION OF THE ELEMENTS IN SPACE It is now an old story, but still possessing its interest, how Fraunhofer analysed the light of the Sun by making it pass through a narrow slit and a prism, and found that the broad rainbow-tinted band of light so obtained was interrupted by hundreds of narrow dark lines, images in negative of the slit; and how Kirchhoff succeeded in proving that two of these dark lines were caused by the white light of the solar photosphere having suffered absorption at the Sun by passing through a stratum of glowing sodium vapour. From that time forward it has been known that the Sun is surrounded by an atmosphere of intensely heated gases, among which figure many of those elements familiar to us in the solid form on the Earth, such as iron, cobalt, nickel, copper, manganese, and the like. These metals, here the very types of solid bodies, are permanent gases on the Sun.