SURVEY OF THE PROBLEM 
11 
/ 
a the constant 
| which from 
> of the aether, 
t of heat. 
3 necessary to 
Dwer in many 
• all chemical 
terior, so that 
i the average 
Dst abundant, 
d is moreover 
The author’s 
ras, however, 
demann that 
;0 a consider- 
1 . Nearly all 
rge; negative 
sitive charge, 
rocess known 
ccessively set 
’he molecular 
age mass per 
the particles 
ibinations of 
the extreme 
light becomes 
the material, 
drogen. 
number Z of 
Z + 1 inde- 
ght 
f the atomic 
i Table 1. 
a much less 
table which 
te complete, 
remain un- 
7 possible to 
make an approximate calculation of the degree of ionisation of the various 
elements under given conditions of pressure and temperature so that the 
amended molecular weights can be found. But the detached electrons 
are so large a proportion of the whole system that the correction is trifling; 
and if we adopt a molecular weight about 2-2 we cannot be far from the 
truth. As the ionisation will diminish with the diminishing temperature 
towards the outside of the star, we may as a refinement adopt a molecular 
weight increasing very slowly from the centre outwards. 
Table 1. 
Average Molecular Weight. 
Element 
Z 
A 
ARZ + l) 
Element 
Z 
A 
ARZ + l) 
Hydrogen 
1 
1 
0-50 
Iron 
26 
56 
2-07 
Helium 
2 , 
4 
1-33 
Silver 
47 
108 
2-25 
Lithium 
3 
7 
1-75 
Barium 
56 
137 
2-40 
Oxygen 
8 
16 
1-78 
Gold 
79 
197 
2-46 
Calcium 
20 
40 
1-91 
Uranium 
92 
238 
2-56 
10 . Having thus resolved the difficulty as to the two constants y and 
¡x, we can obtain numerical values of the temperature, density and pressure 
in a gaseous star of known mass and radius. It will help us to realise the 
conditions that will have to be considered if we now give the results 
obtained for a particular star. For this illustration we choose the brighter 
component of Capella. Capella is the only diffuse (giant) star for which 
the required observational data reach a high standard of accuracy; most 
of the first-class astronomical data refer to dense (dwarf) stars. It is also 
an advantage that Capella is a typical diffuse star, standing about mid 
way in the spectral series. We take the opportunity of explaining (for 
those unfamiliar with double-star astronomy) how the data as to mass, 
luminosity, etc. have been obtained from astronomical observations. 
Capella. 
11 . Capella was discovered to be a spectroscopic binary in 1899 by 
Campbell and Newall independently. The two components are not very 
unequal in brilliancy, so that lines due to both can be seen in the spectrum; 
the two sets of lines are observed to shift to and fro across one another 
owing to the changing Doppler effect as the components approach and 
recede in their orbits. The period is 104-022 days. The full knowledge 
obtained for Capella depends on the fact that it has also been observed 
as a visual double star, and the elements of the visual orbit are believed 
to be well determined. The separation of the two components is only about 
0"-05, which is beyond the resolving power of the largest telescopes adapted