Nipher — Primitive Conditions in the iiolar Nebula. 115 



has reached such a stage in its condensation, that the mass of 

 Neptune is external to Neptune's present orbit. "What will 

 be the condition of the gas at that radius, and what will be 

 the radius H^ of the entire mass M^? At the distance of 

 Neptune's orbit 



J"' X , / 1.029 \ 



0.9975=0.997449. 



By interpolation from the table of integrals above given, 

 this value corresponds to the value of £c = 0.999634. Hence 

 the radius of the nebula is 



li 4.49758X10^^ 

 ^0=^= 0.999634 - 4-49923 X 10^- ■ 



The nebula therefore extends beyond Neptune's orbit a 

 distance of 1.65 X 10^^ cm. or about a million miles. 



This computation cannot of course pretend to any real pre- 

 cision as applied to our special case, since the mass of Nep- 

 tune is so small compared with the mass of the entire nebula. 

 It does apply to a case in which M^ is precisely what we have 

 here assumed it to be. So that we may use this method for 

 exploring the outskirts of such a nebula with a view of learn- 

 ing the physical conditions which must hold in a gaseous 

 nebula. 



If the values now determined be substituted in (56) the 

 value of A is found to be 2.396 X 10^2_ 



The value of A in (51) gives the pressure in C. G. S. 

 units, which, when reduced to atmospheres, is found to be 

 0.000,000,000,149 or 1.49 X lO-^". The same value A in 

 (52) gives for the density at Neptune's place, the value 

 1.93 X 10~^* grammes per cc. These numerical values hold 

 for all gases. The value of CT at this place is therefore 

 7.82 X 10^°. The temperature will therefore depend on the 



nature of the gas. For hydrogen the value of C' = ^p- is 

 4.13 X 10^ The temperature would in that case be about 



