282 THE KEBULAR HYPOTHESIS. 



dies. The quantity of matter contained in the Sun is nearly 

 five miUion times that contained in the smallest planet, and 

 above a thousand times that contained in the largest. And 

 while, from the enormous gravitative force of the atoms, 

 the evolution of heat has been intense, the facilities of ra- 

 diation have been relatively small. Hence the still-contin- 

 ued high temperature. Just that condition of the central 

 body which is a necessary inference from the Nebular Hy- 

 pothesis, we find actually existing in the Sun. 



It may be well to consider a little more closely, what is 

 the probable condition of the Sun's surface. Round the 

 globe of incandescent molten substances, thus conceived to 

 form the visible body of the Sun, there is known to exist a 

 voluminous atmosphere : the inferior brilliancy of the Sun's 

 border, and the appearances during a total eclipse, alike 

 show this.* What now must be the constitution of this at- 

 mosphere ? At a temperature approaching a thousand 

 times that of molten iron, which is the calculated tempera- 

 ture of the solar surface, very many, if not all, of the sub- 

 stances we know as solid, would become gaseous; and 

 though the Sun's enormous attractive force must be a pow- 

 erful check on this tendency to assume the form of vapour, 

 yet it cannot be questioned that if the body of the Sun 

 consists of molten substances, some of them must be con- 

 stantly undergoing evaporation. That the dense gases 

 thus continually being generated will form the entire mass of 

 the solar atmosphere, is not probable. If anything is to be 

 inferred, either from the Nebular Hypothesis, or from the 

 analogies supplied by the planets, it must be concluded 

 ihat the outermost part of the solar atmosphere consists of 

 what are called permanent gases — gases that are not con- 

 densible into fluid even at low temperatures. If we con- 

 sider w^hat must have been the state of things here, when 

 the surface of the Earth was molten, we shall see that 



* See Herschel's " Outlines of Astronomy." 



