284 PHYSICAL SCIENCE 



hypothetical element emitting this light has been 

 named coronium. 



Although recent research has not yet led 

 to a completely satisfactory conception of the 

 general condition of the sun as a physical 

 system, substantial progress in knowledge has 

 nevertheless been made. The gigantic output 

 of heat would be impossible for any solid globe, 

 even if surrounded by a gaseous envelope. The 

 external shell would cool too rapidly, unless a 

 process of convection replaced the cooling gases 

 on the surface by hotter ones from below. The 

 temperature of the sun is above the critical 

 points of most, at any rate, of known substances, 

 and thus, although the pressures may be very 

 high, liquids or solids are probably non-existent, 

 except perhaps as clouds in the upper regions of 

 the atmosphere. The best estimates of the 

 temperature of the radiating part of the sun, 

 based on the amount of solar heat received by 

 the earth, corrected for absorption, agree in 

 indicating a temperature of about 6000^ C. 



A fairly general consensus of opinion had 

 been reached to the effect that the source of the 

 energy required for the sun's continual output of 

 heat was to be sought in the mutual gravitating 

 condensation of his parts. A mass of gravitating 

 gas may become actually hotter by radiation. 

 As it loses heat, its parts approach, and the 

 whole mass contracts. Two bodies attracting 

 each other will, by their collision, set free energy 

 which appears as heat, and the mutual approach 

 of the gravitating parts is an eftect of the same 

 kind. The heat thus developed may be more 



