42 POPULAR THEORIES. 



CHAPTER V. 



POPULAR THEORIES AS TO THE SUN. 



HpHE cause of solar excitation is commonly 

 ascribed to the combustion of gases, or 

 other inflammable substances, such as are used 

 for maintaining beacon fires. This theory in- 

 cludes the question of providing a vast quantity 

 of fuel for supplying such a great conflagration. 

 Newton suggested that the occasional visits of 

 comets near the sun might serve for transporting 

 fuel to sustain the waning supply. Others have 

 suggested that meteoric showers, by continually 

 falling on the orb of the sun, might excite it 

 similarly to the pounding of a bar of iron on an 

 anvil ; by which process blacksmiths sometimes 

 kindle their forge fires. This theory opens the 

 question, " What Cyclops untiringly wields the 

 meteoric hammers?" The combustion of gases 

 is also suggested ; for the existence of hydrogen 

 in the solar orb is indicated by the lines of the 

 spectrum analysis. But the difficulty in the way 

 of this theory is the .want of an adequate supply 

 of free molecules of oxygen, of which eight-fold 

 more is requisite than of the hydrogen ; with the 



