it is difficult to form an opinion as to its existence. Whereas Grebe
and Bachem (Bonn), as a result of their own measurements and those of
Evershed and Schwarzschild on the cyanogen bands, have placed the
existence of the effect almost beyond doubt, while other investigators,
particularly St. John, have been led to the opposite opinion in
consequence of their measurements.
Mean displacements of lines towards the less refrangible end of the
spectrum are certainly revealed by statistical investigations of the
fixed stars; but up to the present the examination of the available
data does not allow of any definite decision being arrived at, as to
whether or not these displacements are to be referred in reality to the
effect of gravitation. The results of observation have been collected
together, and discussed in detail from the standpoint of the question
which has been engaging our attention here, in a paper by E. Freundlich
entitled Zur Prufung der allgemeinen Relativitats-Theorie (_Die
Naturwissenschaften_, 1919, No. 35, p. 520: Julius Springer, Berlin).
At all events, a definite decision will be reached during the next few
years. If the displacement of spectral lines towards the red by the
gravitational potential does not exist, then the general theory of
relativity will be untenable. On the other hand, if the cause of the
displacement of spectral lines be definitely traced to the
gravitational potential, then the study of this displacement will
furnish us with important information as to the mass of the heavenly
bodies.[27]
[27] The displacement of spectral lines towards the red end of the
spectrum was definitely established by Adams in 1924, by observations
on the dense companion of Sirius, for which the effect is about thirty
times greater than for the Sun. R.W.L. translator
APPENDIX IV
THE STRUCTURE OF SPACE ACCORDING TO THE GENERAL THEORY OF RELATIVITY
(SUPPLEMENTARY TO SECTION XXXII)
93