326 SIR F. W. DYSOX, PROF. A. S. EDDINGTON AND MR. C. DAVIDSON ON A 
Plate U. 
Comparison with Oxford Plate Kg. 
Since Plate U shows some good images it has been examined, although owing to the 
absence of star 8 the weight is small. The measures were made at Principe. 
Theoretical plate-constants 
a =+2-8, 6, d=+8-9, e=+37-7. 
Star. 
X. 
Ax. 
AjX. 
+240,y. 
B.,. 
\x. 
Resid. 
11 
1-39 
2905 
2791 
2976 
-101 
- 84 
-147 
4 
17-34 
4508 
4292 
4493 
- 72 
-129 
-192 
3 
17-48 
4626 
4420 
4224 
- 92 
-f288 
+ 225 
6 
19-87 
6270 
5992 
5998 
+ 4 
- 10 
- 73 
10 
22-60 
7110 
6805 
6530 
-P 23 
+252 
+189 
Star. 
X. 
Ay. 
\y- 
—240a;. 
E,. 
Resid. 
11 
12-40 
9026 
8547 
- 334 
+ 6 
8875 
- 94 
4 
18-72 
5846 
4986 
-4162 
+234 
8914 
— 55 
3 
17-60 
5985 
5165 
-4195 
+272 
9089 
+ 120 
6 
24-99 
5458 
4339 
-4769 
+ 136 
8972 
+ 3 
10 
27-21 
4911 
3684 
-5424 
+ 114 
8994 
+ 25 
In this case it is not possible to determine the orientation with sufficient accuracy from 
the ic-measures ; the value here applied is an arbitrary preliminary value. We 
accordingly make a least-squares solution from both x- and ^-residuals to determine 
the correction to the orientation, Sd, as well as Sc, 8/ and 8k. 
The result is 
80=+2, 8k-=+121. 
This gives the deflection 
2"-90. 
The probable error is, however, ± 0"-87, so that the result is practically worthless. 
Further, it is much more likely to be affected by systematic error than the previous 
results. 
The large probable error is partly due to the large residuals which are greater than 
in the previous measures ; in particular star 3 is unduly faint. If the same accuracy 
had been obtained, the theoretical weight would have been half that of plates W and X : 
