120
WEIGHING LIGHT
[CH.
A diagram showing the relative positions of the stars is given in Fig. 18.
The square shows the limits of the plates used at Principe, and the oblique rectangle the limits with the 4-inch lens at Sobral. The centre of the sun moved from to in the 214
hours interval between totality at the two stations; the sun is here represented for a time about midway between. The stars measured on the Principe plates were Nos. 3, 4, 5, 6, 10, 11; those at Sobral were 11, 10, 6, 5, 4, 2, 3 (in the order of the dots from left to right in Fig. 17). None of these were fainter than 6m.0, the brightest κ1 Tauri (No. 4) being 4m.5.
It has been objected that although the observations establish