KNOWLEDGE OF THE SUN — ST. JOHN 189 



will eventually escape from the sun with enormous velocities. Tlie 

 velocities of tlesceiit are hardly likely to exceed the velocities of 

 thermal agitation. When the Fraunliofer spectrum is observed, 

 there are therefore more atoms absorbing from the red wing than 

 from the violet. Hence the absorption line will appear displaced to 

 the red, and this feature should become more prominent with in- 

 creasing height (Milne, Merfield). The displacements to the violet 

 at low levels seem explicable by the upward streaming of gases near 

 the photosphere. 



The last three columns show respectively the very low pressure 

 in the sun's atmosphere by which the sun again shows its similarity 

 to the stars, the rotation at dili'erent levels, and tlie heights to which 

 the different gases rise as derived from the eclipse observations. 



RELATIVITY 



The question of the gravitational displacement of the Fraunhofer 

 lines predicted by the general theory of relativity has been a subject 

 of extended investigation, with the result that when other known 

 characteristic displacements in stellar atmospheres are taken into 

 consideration the remaining displacements to the red universally 

 observed are most satisfactorily interpreted in accordance with that 

 theory (Evershed, St. John). The interpretation is reinforced by 

 the observed eflfect in the " white dwarf " companion of Sirius by 

 Adams and Moore. 



This brief outline of the progress in our understanding of the 

 sun illustrates the wide-reaching results in astrophysical investiga- 

 tions from the union between spectroscopic observations on the sim, 

 work in the physical laboratory, and deductions from atomic theory, 

 and perhaps justifies the claim of astrophysics that it deals with 

 the most interesting questions of physical research. 



