DETERMINATION OF DEFLECTION OF LIGHT BY THE SUN’S GRAVITATIONAL FHHJ). 331 
The result from declinations is about tudce the weight of that from right ascensions, 
so that the mean result is 
l"-98 
with a probable error of about ±0"-12. 
The Principe observations were generally interfered with by cloud. The unfavourable 
circumstances were perhaps partly compensated by the advantage of the extremely 
uniform temperature of the island. The deflection obtained was 
1"-61. 
The probable error is about ±0"-30, so that the result has much less weight than 
the preceding. 
Both of these point to the full deflection 1"*75 of Einstein’s generalised relativity 
theory, the Sobral results definitely, and the Principe results perhaps with some un¬ 
certainty. There remain the Sobral astrographic plates which gave the deflection 
0"-93 
discordant by an amount much beyond the limits of its accidental error. For the 
reasons already described at length not much weight is attached to this determination. 
It has been assumed that the displacement is inversely proportional to the distance 
from the sun s centre, since all theories agree on this, and indeed it seems clear from 
considerations of dimensions that a displacement, if due to gravitation, must follow this 
law. From the results with the 4-inch lens, some kind of test of the law is possible 
though it is necessarily only rough. The evidence is summarised in the following table 
and diagram, which show the radial displacement of the individual stars (mean from all 
the plates) plotted against the reciprocal of the distance from the centre. The displace¬ 
ment according to Einstein s theory is indicated by the heavy line, according to the 
Newtonian law by the dotted line, and from these observations by the thin line. 
Radial Displacement of Individual Stars. 
Star. 
Calculation. 
Observation. 
11 
ff 
0-32 
r/ 
0-20 
10 
0-33 
0-32 
6 
0-40 
0-56 
5 
0-53 
0-54 
4 
0-75 
0-84 i 
2 
0-85 
0-97 1 
3 
0-88 
1 -02 
1 
1 
2 z 
VOL. CCXX.—A. 
