The distortions of the solar lines indicate that the wind at the surface of the sun often blows with a velocity of _from one hundred to three hundred miles a second_. The most violent wind known on the earth has velocity of a hundred miles an hour. III. THE PHOTOSPHERE AND SUN SPOTS. The Photosphere. [Illustration: Fig. 190.] 172. _The Granulation of the Photosphere._--When the surface of the sun is examined with a good telescope under favorable atmospheric conditions, it is seen to be composed of minute grains of intense brilliancy and of irregular form, floating in a darker medium, and arranged in streaks and groups, as shown in Fig. 190. With a rather low power, the general effect of the surface is much like that of rough drawing-paper, or of curdled milk seen from a little distance. With a high power and excellent atmospheric conditions, the _grains_ are seen to be irregular, rounded masses, some hundreds of miles in diameter, sprinkled upon a less brilliant background, and appearing somewhat like snow-flakes sparsely scattered over a grayish cloth. Fig. 191 is a representation of these grains according to Secchi. [Illustration: Fig. 191.] With a very powerful telescope and the very best atmospheric conditions, the grains themselves are resolved into _granules_, or little luminous dots, not more than a hundred miles or so in diameter, which, by their aggregation, make up the grains, just as they, in their turn, make up the coarser masses of the solar surface. Professor Langley estimates that these granules constitute about one-fifth of the sun's surface, while they emit at least three-fourths of its light. 173. _Shape of the Grains._--The grains differ considerably in shape at different times and on different parts of the sun's surface. Nasmyth, in 1861, described them as _willow-leaves_ in shape, several thousand miles in length, but narrow and with pointed ends. He figured the surface of the sun as a sort of basket-work formed by the interweaving of such filaments. To others they have appeared to have the form of _rice-grains_. On portions of the sun's disk the elementary structure is often composed of long, narrow, blunt-ended filaments, not so much like willow-leaves as like bits of straw lying roughly parallel to each other,--a _thatch-straw_ formation, as it has been called. This is specially common in the immediate neighborhood of the spots. 174. _Nature of the Grains._--The grains are, undoubtedly, incandescent _clouds_ floating in the sun's atmosphere, and composed of partially condensed metallic vapors, just as the clouds of our atmosphere are composed of partially condensed aqueous vapor. Rain on the sun is composed of white-hot drops of molten iron and other metals; and these drops are often driven with the wind with a velocity of over a hundred miles a second.