182 ON THE ORIGIN OF THE PLANETAKY SYSTEM. 



temperature might be raised to 28,000,000 of degrees, 

 if this quantity of heat could ever have been present 

 in the sun at one time. This cannot be assumed, for 

 such an increase of temperature would offer the 

 greatest hindrance to condensation. It is probable 

 rather that a great part of this heat, which was pro- 

 duced by condensation, began to radiate into space 

 before this condensation was complete. But the heat 

 which the sun could have previously developed by its 

 condensation, would have been sufficient to cover its 

 present expenditure for not less than 22,000,000 of 

 years of the past. 



And the sun is by no means so dense as it may 

 become. Spectrum analysis demonstrates the presence 

 of large masses of iron and of other known constituents 

 of the rocks. The pressure which endeavours to con- 

 dense the interior is about 800 times as great as that 

 in the centre of the earth ; and yet the density of the 

 sun, owing probably to its enormous temperature, is 

 less than a quarter of the mean density of the earth. 



We may therefore assume with great probability 

 that the sun will still continue in its condensation, even 

 if it only attained the density of the earth though it 

 will probably become far denser in the interior owing 

 to the enormous pressure this would develop fresh 

 quantities of heat, which would be sufficient to main- 

 tain for an additional 17,000,000 of years the same 



