162 Liquid Stars [ch. v 
that at the right-hand edges of the areas of stability the gas-laws are approxi 
mately obeyed, so that there will be no very great error involved in supposing 
the gas-laws to be obeyed at this point. The point is generally agreed to be 
about absolute bolometric magnitude +1 and spectral type F. The value 
of X for stars at this point is about 3. At this point by equation (140’2), 
= 1-52 x 10 5 (148-1). 
o- (t + l) 3 
The point is a minimum for L -ring ionisation, so that we must put a = 8 
and t + 1 = 2 in this equation. Putting X = 3 we find that 
A = 93-9 (148-2). 
Equation (148T) assumes the gas-laws to be obeyed. We have seen that 
the effect of deviations from the gas-laws is to extend the range within which 
the minimum exists. Thus if the true value of X at this point is 3, the value 
which satisfies equation (1481), which is the value before the range is 
extended, must be somewhat less than 3, so that the value of N must be 
somewhat higher than 93"8. 
149. The other coordinate of the selected point is fixed by equation 
(140-4). The value of Q is known to be 27,200 at this point, so that the 
equation takes the form 
T(t+ 1) 2 = 27,200A 2 (1491), 
and on putting t+1=2, and T= 60,000,000, this being the approximate 
central temperature of stars at this point, we find 
N = 93-2 (149-2). 
The agreement between these two values of N is entirely satisfactory, but 
it cannot be claimed that the value of N can be determined with anything 
like the accuracy suggested by small differences between these determinations. 
It appears, however, that the atomic numbers of stellar atoms are in the 
neighbourhood of, and possibly slightly higher than, those of the radioactive 
elements, and this fits in well with the conclusions to which we were led in 
the last chapter as to the generation of stellar energy. We could equally 
well have determined A by using equation (149*1) in its more general form 
T(r-(-l) 2 =QA 2 (149-3), 
and applying it at a point higher up the main sequence. We have already 
seen that as we advance up the main sequence the values of T which are 
calculated from observation increases slightly, while theory compels the value 
of Q to increase slightly. Actually the value of T appears to increase rather 
more rapidly than that of Q, so that the values of A calculated from 
equation (149"3) would increase as we pass up the main sequence—i.e. A 
would be greater for younger stars than for older. This again is entirely in 
agreement with our conclusions as to the generation of stellar energy, but the 
increases in A are too slight for us to lay much stress on them.