120 Trans. Acad. Sci. of St. Louis. 



This shows that in a cosmical gas-kugel of such mixed 

 gases, the particular isothermal which at any time during 

 the contraction of the nebula is at a distance R =0.901 JR Q , 

 will then be at its maximum. Isothermals internal to this 

 will be increasing in radius, while those outside will be con- 

 tracting. This condition is due to the fact that the outer 

 limit of the nebula has a constant temperature of zero. The 

 isothermals originate at the center and enlarge as the con- 

 traction proceeds, while the inward motion due to contraction 

 is greatest at the external surface, and approaches zero at 

 the center. When an isothermal has reached a radius 

 0.901 Ii , it continues to approach the outer limit of the 

 nebula, but on account of contraction, its radius is really 

 diminishing. The temperature of this particular isothermal 

 may be computed from (59). 



The isothermal of 7000° C. is now probably at the surface 

 of the sun. If the solar system had been evolved from a 

 gaseous nebula from its early stages, this isothermal would 

 have reached its maximum radius, when the radius of the 

 nebula, i? = 3.09 X 10 15 cm. This is about one thousandth 

 of the distance to a Centaur! . The radius of the isothermal 

 itself was 0.901 i? . 



Equation (57) should apparently enable us to compute 

 what may perhaps be called the height of the solar atmos- 

 phere. This is the present distance from the isothermal 

 7000° to the outer limit of the solar mass where the pressure 

 is zero. Let C =2.88X 10 6 which is the constant for air. 

 Let M Q = 1.987 X 10 33 , which is the solar mass in grammes. 

 The solar radius will be taken as Ii n = 6.961 X 10 10 cm. The 



gravitation constant = 1 ^^ 1010 • Then is 



0.9975' 



n '^l.oixio- 73 



(2 — n 2 JcM Q 



The value of x for this isothermal in such a nebula, having 



