Physics. — “The General Relativity Theory and the Solar Spectrum’. 
By Prof. W. H. Junius and Dr. P. H. van Cirrert. 
(Communicated at the meeting of May 29, 1920). 
Of the three crucial inferences drawn by Einstein from the general 
relativity theory, which should make it possible to decide whether 
that theory conforms more closely than the old ideas to the results 
of most subtile observation, two seem to have stood the test success- 
fully. As to the third deduction — a systematic displacement of the 
Fraunhofer lines towards the red — evidence is still wanting. 
This uncertainty is not due to the smallness of the expected effect. 
Displacements of Fraunhofer lines with respect to the corresponding 
lines in the spectra of terrestrial sources have been measured in 
abundance; they are similar in magnitude to the “gravitational shift” 
required by the relativity theory, the latter shift averaging ten times 
the unity (0,001 A) in which the measured displacements are gene- 
rally expressed. But the simple law which, according to the theory, 
should connect displacements with wave-lengths, does decidedly not 
show itself in the direct results of observation; the difficulty, indeed, 
lies in the fact that several other causes (such as motion in the line 
of sight, pressure, anomalous dispersion) may co-operate, each capable 
of producing displacements of the same order of magnitude. 
One should, therefore, attempt to group and analyze the obser- 
vational data in such a way, that all influences except the EINSTEIN 
effect are eliminated or accounted for. This can be done, at least up 
to a certain point, because the said causes of displacement act 
according to different laws. 
Attempts have already been made to exclude the effect of pressure. 
ScHWARZSCHILD'), EversHeD and Royps?), St. JonN®, GRrBE and 
Bacnem*) selected for the investigation lines of which it was known 
that, in the laboratory, they did not show any appreciable pressure 
effect. The results obtained by these observers do not agree. Accord- 
1) K. ScHWARZSCHILD, Berl. Ber. 1914, S. 1201. 
2) EVERSHED and Royps, Kodaikanal Bull. 39, 1914. 
3) Sr. Jon, Astroph. Journ. 46, 246, (1917); Mt. Wilson Contrib. NO. 138. 
4) GREBE and Bacuem, Verh. d. D. Phys. Ges. 21, 454 (1919); Zeitschr. f. 
Physik. 1, 51 (1920). 
