164 



ANNUAL REPORT SMITHSONIAN INSTITUTION, 1937 



show that circulation is going on all over the sun. These motions 

 cause Doppler sliifts which affect exact wave lengths. In what 

 follows some consequences will be noted, particularly as they are 

 correlated with intensities and heights determined from eclipse spectra. 



THE PRINCIPLE OF RELATIVITY 



Einstein's theory of gravitation has been justly regarded as the 

 greatest triumph of mathematical reasoning since the time of Newton. 

 It is safe to say that no scientific achievement of recent years has 

 aroused so much popular interest and enthusiasm as that evoked by 

 the verification of the Einstein prediction by the 1919 total eclipse. 

 In addition to the shift in star light by the gravitational pull of the 

 sun amounting to \" .12 at the sun's edge, the principle of relativity 

 has two other consequences shown by: (1) The motion of perihelion 

 of the i)lanet Mercury; and (2) the red shift of lines in the solar 

 spectrum. We shall first take up the shift to longer wave lengths. 



The Allegheny Observ'^atory in cooperation with the Bureau of 

 Standards has determined laboratory wave lengths of the highest 

 degree of reliability. The method of obtaining the photographs was 

 by a powerful gratmg spectrograph and interferometer, the wave 

 lengths having an accuracy of 1 part in 5,000,000. For many reasons 

 the results for neutral iron are more exact than for any of the elements. 

 Wave lengths m the laboratory reduced to the conditions of vacuum 

 pressure are referred to as "vacuum arc." Differences in wave length 

 between the sun and the vacuum arc, after the greatest care is exer- 

 cised to get all wave lengths to the one standard system, are given 

 in the foUowuig table. From the differences, sun minus vacuum 

 arc, are subtracted the predicted relativity shift amounting to 

 2.13X10~®XX where X is the wave length in angstroms. 



Tadle 1. — Relativity shift in the sun 



