deviation is taken from Einstein’s computed value of 1″.75. In the second line the difference shown is from the value required by the Newtonian theory, 0″.87. The results obtained with this telescope were rejected however, although they were much the most numerous, because it was found that for some reason, supposed to be the heating of the mirror by the sun before the eclipse, the star images were slightly out of focus, and were therefore considered unreliable. The results with the two other telescopes were not very accordant, but the 4-inch had the longer focus, secured the greater number of plates, and showed the greater number of stars. The results obtained with it therefore appear to have been the more reliable. They differ from Einstein’s prediction by 13 per cent. In future expeditions to test this question, the mirror in front of the telescope will be eliminated.

We now come to the final test which has been applied to Einstein’s theory. Einstein showed that in the intense gravitational field of the sun, the theory of relativity required that all of the spectrum lines should be shifted slightly toward the red end. The shift however is exceedingly small, and can only be detected and measured with the most powerful modern instruments. Moreover only certain lines can be used, because owing to varying pressure in the solar atmosphere, which affects many lines, as well as to rapid motion in the line of sight, which may affect all of them, still larger displacements are liable to occur.

According to the theory of relativity the displacement of the lines should be

. St. John at Mt. Wilson found a displacement for the cyanogen lines of only

.[16] Evershed at Kodaikanal found +0.0060 at the north pole of the sun, and +0.0080 at the south pole. These latter values however were only for the stronger lines. The weaker lines give much smaller shifts, as do those of calcium and magnesium.[17] According to Einstein all lines should give nearly the same shift, an amount proportional to the wave length. It therefore appears that we must conclude by saying that Einstein’s theory of relativity has been partially, but not completely, verified.

The reference numbers in the above text have nothing to do with the numbers used in other parts of this volume to acknowledge the work of the various contestants; they refer to Dr. Pickering’s sources, as follows:

[1] Journ. Brit. Astron. Assoc., 1919, 30, 76.

[2] Comptes Rendus, 165, 424, and 167, 71.