DEFLECTION OF LIGHT DYSON AND OTHERS. 
151 
further measurement. The mean values ^C.G^^*" 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 in- 
strumental conditions, but there is the difference that the eclipse 
photographs were taken on the day of May 29, and the comparison 
photographs on nights between July 14 and July 18. A very satis- 
factory 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 correc- 
tions for differential refraction and aberration are calculated from 
the times and dates of exposure. 
Eclipse plates... 
Scale plate 
Comparison 142a 
142/, 
15i.. 
15a.. 
17i.. 
17s.. 
I82.. 
+0. 240 
+ .423 
+ .409 
+ .409 
+ .390 
+ .370 
+ .399 
+ .337 
+ .327 
+0. 168 
+ .207 
+ .207 
+ .207 
+ .207 
+ .202 
+ .207 
+ .202 
+ .202 
+0. 002 
+ .096 
+ .091 
+ .091 
+ .0S7 
+ .087 
+ .091 
+ .077 
+ .072 
+ 0.062 
+ .096 
+ .091 
+ .091 
+ .087 
+ .087 
+ .091 
+ .077 
+ .072 
When these are applied to the values of the constants found from 
the normal equations we find the following values of the scale of the 
several photographs and their orientation relative to the scale plate : 
EcUpse I 
II 
Ill 
IV 
V 
VII 
VIII 
Comparison 142a 
1426 
15i.. 
15j.. 
17j.. 
17j.. 
18j.. 
Scale value. 
From X. From y. 
-0. 
-0. 010 
- .024 
+ .053 
+ .006 
- .006 
+ .017 
+ .031 
+ .004 
+ .030 
- .085 
- .075 
- .077 
- .109 
- .087 
Orientation. 
From I. From y 
-0.237 
- .045 
-I- .014 
- .027 
+ .008 
+ .032 
+ .008 
+ . 081 
- .035 
+ . 155 
+ .003 
- .116 
+ .062 
- .014 
-0. 265 
- .107 
+ .025 
- .040 
+ .031 
+ .050 
+ .006 
+ .033 
- .049 
+ . 086 
- .035 
- .174 
+ .029 
- .074 
Adopted scale and 
orientation. 
0.000 
0.000 
0.000 
0.000 
0.000 
0.000 
0.000 
+0. 013 
+ .013 
- .084 
- .084 
- .084 
- .084 
- .084 
-0. 251 
- .076 
+ .020 
- .034 
+ .020 
+ .041 
+ .007 
+ .057 
- .042 
+ .120 
- .016 
- .145 
+ .046 
- .044 
