MODERN THEORIES OF THE SUN—BOSLER. 157 
to it a duration in the future of several hundred billion centuries with 
the present loss of energy by radiation. It would then without doubt 
die of good old age unless destroyed by direct collision with some 
other star.t. But let us not trouble ourselves about this and come 
back to our subject. 
INTERIOR EQUILIBRIUM OF THE SUN. 
A mass of gas subject only to the mutual gravitation of its parts, 
such as is the sun, tends to assume a spherical shape. The resultant 
of the attracting forces at each point is then directed toward the 
center. However, there are two particular ways in which this equi- 
librium may become established. In an immobile fluid the temper- 
ature can be equalized only through conductivity, and if that is 
high, the temperature will everywhere be finally the same. This is an 
isothermal equilibrium. If, on the other hand, the fluid mass is subject 
to convection currents and the conductivity is negligible, the temper- 
ature will differ at different places and depend upon the local pressure.? 
This is an adiabatic equilibrium. 
Now, the sun is gaseous and gases are generally very poor con- 
‘ductors for heat. Moreover, the loss of heat by radiation is relatively 
very small. Further, the sun seems subject to incessant movements 
of which the spots and facyle are evidence. Therefore, it must be 
in adiabatic equilibrium. Postulating this, we may study mathe- 
matically the distribution of pressures and temperatures in the 
interior of a star formed thus of a perfect gas when we know its total 
mass, its mean density and peripheral pressure (supposed to be zero). 
With these data known, the problem admits of solution and the 
pressures and temperatures will be found to increase very rapidly 
toward the center. For instance, for a sun composed of hydrogen, 
assumed monatomic at high temperatures, the density at the center 
will be about 8, the pressure 8 billion atmospheres, and the temper- 
ature 24 million degrees. Similar calculations give for other gases 
results of the same order of magnitude. This is all we may hope to 
obtain. 
One point to be noted is that all this assumes an apparent contour 
to the sun, which takes away from Schmidt’s theory one of its most 
_ seducing advantages. But there is something better: The sun radi- 
ates toward us and yet the quotient of the heat lost by the lowering 
of the temperature may in certain cases be negative; that is, the 
more heat the sun sends to us the warmer it may get. This is called 
the ‘paradox of Lane” and it is a good one. However, we have 
here a complex effect very analogous to the accelerating action of a 
1 Such as was considered by .M. P. Salet in his article in the Revue du Mois (1911), ‘‘Le soleil doit-il 
s’éteindre?’”’ (Will the sun become extinguished ?). 
2 A gas compressed in a receiver impermeable to heat becomes heated, when expanded, cooled. 
