DEFLECTION OF LIGHT—DYSON AND OTHERS. - 15] 
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 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. 
a. é db. d. 
T T 
BH PSONDIAGCS yee) ner (oa eter eect es +0. 240 +0. 168 +0, 062 +0. 062 
SGELD [LURES SABES LE eh Bea id se i tiie Be Sale + .423 + .207 + .096 + .096 
ontysrisOn 14h). vi2ae sees eee eke segn = aes eteabinn - + .409 + .207 + .091 + .091 
V4gp:------- 222-2 2 eee eee ++ . 409 + .207 + .091 + .091 
1b) Bee: Ase eee ee Seeee eee eee een sno eoe + .390 + .207 + .087 a eOsT 
iy PA e sec aeeee 348 Gee Eno eae See See See + .370 + .202 + .087 ++ .087 
oY RR ones e eee Sine eee ene te ae + -399 + ..207 + .091 ++ .091 
17... -------------- 2222222 eee eee eee + .337 + .202 + .077 + .077 
Lohpesans Gaddos dct sosedepeaecdsecracen sabe + £327 + .202 + 2072 + .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: 
Scale value. Orientation. 
Adopted scale and 
orientation. 
From z. From y. From 2. From y. |° a Q 
r T r T 
MICH pPsetT Ios Ie- wee =) TRE 5 ese —0. 025 —0. 010 —0. 237 —0. 265 0.000 —0. 251 
1 A ee el eee a — .009 — .024 — .045 r=. 107 0.000 — .076 
ITE eR Laie +..006 + .053 + .014 + .025 0.000 + .020 
NTN fh NS oe oe ae — .056 + .006 — .027 — .040 0.000 — .034 
AV) ee en Bae gee — .055 — .006 + .008 + .031 0.000 + .020 
VALE RES Bese Mae + .050 +. .017 + . 032 + .050 0.000 + .041 
S00 015 Sa Pee eee See — .014 + .031 + . 008 ++ . 006 0.000 + .007 
Comparison 149g....--.-----.-- + .010 + .004 + .081 + . 033 +0, 013 + .057 
Ey ee or ee eas + .018 + .030 — 035 — .049 + .013 — .042 
Gop ko deee sens —.. 063 — .085 + 155 + . 086 — .084 + .120 
LS eae re et ome — .065 — .075 + .003 — .035 — .084 — .016 
LR SESSA. Joe — .118 — .077 — .116 — .174 — .084 — .145 
WC ASE ee, a — .072 — .109 + .062 + . 029 — .084 + .046 
TSP eats © = Cees aaa — .093 — . 087 — .014 — .074 — .084 
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