Letter | Published:

The Displacement of Light Rays Passing near the Sun

Nature volume 104, page 354 (04 December 1919) | Download Citation



THE part of the earth's atmosphere within the conical shadow of the moon during a total solar eclipse may be regarded as approximately a right circular cylinder, the area of the base of which depends on the length of the shadow. Observations have shown that there are temperature and pressure gradients in this cylinder. The latter gradient at the surface of the earth is usually slight, but the temperature gradient may be considerable, so that, assuming that there is equilibrium, we have, roughly speaking, a cylinder of air the density of which decreases outwards in all directions perpendicular to its axis. When we remember that the light from stars at small angular distances from the sun's centre makes small angles with the axis of this cylinder, it is easy to see that a very small density gradient would be sufficient to account for the displacements that were observed in the total solar eclipse of the present year.

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  1. University College, Galway.



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