It may be added that, according to the theory, half of this deflection is produced by the Newtonian field of attraction of the sun, and the other half by the geometrical modification ("curvature") of space caused by the sun.
FIG. 5.
This result admits of an experimental test by means of the photographic registration of stars during a total eclipse of the sun. The only reason why we must wait for a total eclipse is because at every other time the atmosphere is so strongly illuminated by the light from the sun that the stars situated near the sun's disc are invisible. The predicted effect can be seen clearly from the accompanying diagram. If the sun (
) were not present, a star which is practically infinitely distant would be seen in the direction
, as observed from the earth. But as a consequence of the deflection of light from the star by the sun, the star will be seen in the direction
, i.e. at a somewhat greater distance from the centre of the sun than corresponds to its real position.