30G SIR F. W. DYSON, PROF. A. S. EDDINGTON AND MR. C. DAVIDSON ON A 
21. The values of a are collected in Table VII :— 
Table VII. 
Right Ascension. 
Declination. 
Eclipse — Scale. 
Comparison — Scale. 
Eclipse — Scale. 
Comparison — Scale. 
r 
r 
r 
r 
+0-098 
+0-042 
+0-126 
+0-044 
+0-126 
+0-024 
+0-139 
+0-007 
+0-107 
-0-015 
+0-114 
+0-021 
+ 0-148 
+0-018 
+0-111 
+0-010 
+0-140 
+0-020 
+0-137 
+0-040 
+0-073 
+0-005 
+0-139 ■ 
+0-060 
+0-145 
+0-008 
+0-136 
+0-036 
Mean +0-120 
+0-015 
+0-129 
+0-031 
By subtracting the a of the comparison plates the scale plate is eliminated, and we 
derive from right ascensions a = H-0'’-l05 and from declinations a = +0''-098. 
Reference to the normal equations shows that the declination result is of double 
the weight of that from the right ascensions. 
Thus 
a +0’'-100 = +0"-625. 
This is at a distance 50' from the sun’s centre. At the time of the eclipse the sun’s 
radius was 15'-8 ; thus the deflection at the limb is 1"‘98. 
The range in the values of a is attributable to the errors inherent to the star images of 
the different plates, and cannot be reduced by further measurement. The mean values 
+0’'-015 and 0’'-031 arise from the errors in the intermediary scale plate. 
22. The probable error of the result judging from the accordance of the separate 
determinations is about 6 per cent. It is desirable to consider carefully the possibility 
of systematic error. The eclipse and comparison photographs were taken under 
precisely similar instrumental conditions, but there is the difference that the echpse 
photographs were taken on the day of May 29, and the comparison photographs on 
nights between July 14 and July 18. A very satisfactory feature of the photographs 
is the essential similarity of the star images on the two sets of photographs. 
The satisfactory accordance of the eclipse and comparison plates is shown by a study 
of the plate constants. The following corrections for differential refraction and 
aberration are calculated from the times and dates of exposure. 
