402 POPULAR LECTURES AND ADDRESSES 



depths inwards from the bounding surface the 

 temperature is becoming higher and higher. This 

 would certainly be the case if the gaseous law of 

 condensation held throughout, but even then the 

 effective radiational temperature, in virtue of which 

 the sun sheds his heat outwards, might be be- 

 coming lower, because the temperatures of equi- 

 dense portions are clearly becoming lower under 

 all circumstances. 



Leaving now these complicated and difficult 

 questions to the scientific investigators who are 

 devoting themselves to advancing the science of 

 solar physics, consider the easily understood 

 question, What is the temperature of the centre 

 of the sun at any time, and does it rise or 

 fall as time advances ? If we go back a few 

 million years, to a time when we may believe the 

 sun to have been wholly gaseous to the centre, 

 then certainly the central temperature must have 

 been augmenting ; again, if, as is possible though 

 not probable at the present time, but may probably 

 be the case at some future time, there be a solid 

 nucleus, tnen certainly the central temperature 



