COSMICAL GEOLOGY. 157 



state of vapour. Kirchhoff then suggested that clouds formed 

 in the white-hot photosphere, and that these clouds became 

 darker as they cooled, thus giving origin to the appearance of 

 sun-spots. 



Zollner contested this hypothesis on the ground of the rela- 

 tively small variation in the shape of the spots, and agreed with 

 the explanation given by Fabricius. Reye and Faye regarded 

 the sun-spots as a result of cyclones in the lower region of the 

 sun's atmosphere. There can be no doubt that storm move- 

 ments take place at the surface of the sun. This was made 

 evident when Sir Norman Lockyer in 1869, and in his later 

 work on Solar Physics (1873), demonstrated the presence of a 

 mantle of glowing vapour from which there projected gigantic 

 torch-like protuberances subject to violent movement. Lockyer 

 called the outer mantle of the sun " chromosphere " on account 

 of its red colour. 



All the modern theories about the constitution of the sun 

 agree in assuming that it must have received an immeasurably 

 great supply of heat during its condensation, and that already 

 a considerable quantity has been lost by radiation. Neverthe- 

 less, the sun is still in a white-hot condition, and replaces the 

 loss of heat by continued condensation and by absorption of 

 matter attracted from sidereal space. The spectroscopical 

 researches of Kirchhoff, Secchi, Zollner, Lockyer, Young, and 

 others, have demonstrated that more than half of the terrestrial 

 elements are present in the composition of the sun. 



In the present position of astronomical research there is no 

 precise means of determining the temperature of the sun, 

 although its size and density are well known. The sun is 

 more than a hundred times larger than the earth, but has only 

 a quarter of the earth's density. It follows from the continuity 

 of the sun's spectrum that the sun's nucleus is incandescent, 

 but it is difficult to decide whether the material is in a liquid 

 state, as Kirchhoff and Zollner suppose, or whether Secchi 

 and Faye may be correct in supposing the nucleus to be for 

 the most part gaseous, including some denser portions in a 

 state of stormy movement. 



The Fixed Stars and Planets. While the sun represents 

 a celestial body not yet fully consolidated, although in an 

 advanced stage of condensation, the nebulae, fixed stars, and 

 planets give indication of the phases of development through 



