[ch. m 
72 Gaseous Stars 
The value of R/rrifi for atmospheric air is 2'87 x 10 6 , so that 
0 = 1*1226 x 10 8 degrees ( 66 ’ 2 ). 
This, as we have seen, would be the temperature at a point inside the 
model sun at which the density is unity. From this it follows at once that 
the temperature, density and pressure at the sun’s centre are: 
Temperature at centre of sun = 455 million degrees. 
Density „ „ „ „ = 34 , 02. 
Pressure „ „ „ „ = 4 3 x 10 16 dynes. 
= 43,000 million atmospheres. 
Ionisation in Stellar Interiors. 
67. These last figures refer only to a very special model of a single star, 
but calculations for other stars and other models give very similar tempera 
tures for stellar centres. A large number of detailed calculations will be found 
in Emden’s book. As was first pointed out by the present writer in 1917*, 
neither molecules nor atoms could retain their existence as such at temperatures 
as high as this. Whatever model we take, a simple calculation shews that the 
temperature throughout the greater part of a star’s interior must produce a 
very high degree of electronic dissociation, the molecules and atoms being 
almost completely broken up into their constituent electrons and nuclei, 
which will now all move about independently like the molecules of a gas. In 
more peaceful surroundings their electrostatic attractions would rapidly unite 
the wandering nuclei and electrons into complete atoms and molecules, but 
these are powerless in the general whirl of rapidly moving projectiles and in 
face of the shattering blows of the quanta of high-frequency radiation which 
the high temperatures of the stellar interiors generate. It is no more possible 
to build up an atom in the interior of a star than to build a house of cards in 
a hurricane. 
When I first put forward this view I believed it to be entirely novel, but 
I have since found that in 1644 Descartes had conjectured*}* that the sun and 
fixed stars were made of matter “which possesses such violence of agitation 
that, impinging upon other bodies, it gets divided into indefinitely minute 
particles.” 
68 . This view of the constitution of stellar interiors reduces the central 
temperature to a value far below that just calculated. 
In breaking up a molecule of, say, nitrogen into its ultimate constituents, 
we replace a single moving unit by sixteen separately moving parts, two 
positive nuclei and fourteen free electrons. If the temperature remains un 
altered each of these sixteen parts exerts, statistically, the same pressure 
as the original molecule, so that the pressure corresponding to a given 
* Observatory , xl. (1917), p. 43 and Bakerian Lecture (1917), Phil. Trans. 218 a, p. 209. 
f Principiorum Philosophiae , Part in, Chap. 52.