DEFLECTION OF LIGHT — DYSON AND OTHERS. 
171 
probable error ±0.14" in the final result ; or, if we adopted the largest 
(rather discordant) value found for e' instead of the mean, we 
should reduce the result by 0.52". 
An error of 10 units in the orientation gives an error in the result 
of 0.45" for plate X, and 0.22" for plate W. It is therefore of less 
importance, and further it is not likely to be systematic. 
Errors in the measurement of x only affect the result through the 
orientation. For plate X, a probable error of ±0.20" in the ad- 
measures would give an error ±4.0 in the orientation, leading to an 
error ±0.18" in the result; whereas an error of the same magnitude 
in the y-measures gives directly an error ±0.35" in the result. For 
plate W, the probable error of ±0.20" in x gives an error ±3.5 in the 
orientation and ±0.08" in the result, compared with ±0.38" for 
similar inaccuracy in y. It is particularly fortunate that the a?-meas- 
ures are so unimportant for plate W, because, as already mentioned, 
the images trailed on that plate. 
Finally, it will be remembered that in order not to commit our- 
selves to the Einstein hypothesis prematurely we neglected the correc- 
tion iEa. in determining the orientation. This will make a difference 
of 0.029" in the results from plate W and 0.092" from plate X. The 
effect is that the deduced deflection needs to be decreased, and the 
mean correction —0.06" should be applied to the mean result obtained 
or rather to make the adopted deflection for x consistent with the 
deduced value from y, the correction needed is —0.04". 
DISCUSSION or THE RESULTS. 
The four determinations from the two eclipse plates are 
X— G 1.94" 
X— H 1.44" 
W— D 1.55" 
W— I 1.67" 
37. 
Giving a mean of 1.65" 
They evidently agree with Einstein's predicted value 1.75". 
The residuals ^^ in the separate comparisons reduced to arc are as 
follows. The do not appear to show any special pecularities : 
I 
-residuals 
!/ 
-residuals 
star. 
G. 
H. 
D. 
I. 
Mean. 
G. 
H. 
D. 
I. 
Mean. 
11 
+0. 0-I 
-0.05 
-0.30 
+0. IG 
+0.14 
+0.70 
-0.50 
-0.40 
+0.30 
-0.09 
" 
" 
" 
+0.01 
-0.16 
+0.41 
-0.34 
+0.07 
+0.52 
-0.11 
+0.07 
-0.20 
-0.27 
" 
" 
" 
5 
+0.12 
-0.18 
-0.13 
-0.54 
+0.73 
+0.14 
+0.02 
-0.32 
-0.13 
+0.27 
-0.07 
-0.21 
0.00 
-0.16 
+0.21 
-0.22 
+0.33 
-0.39 
+0.07 
-0.04 
-0.32 
+0.10 
-0.08 
+0.35 
-0.02 
4 
-0.02 
3 
-0.03 
6 
-0.17 
10 
13 The residuals refer to the theoretical deflection 1.75", not the deduced deflections. 
