Letter | Published:

Gravitation and Light

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



As I said last week (p. 334), and also in the December Phil. Mag. (p. 737), the refractivity μâ1, necessary at every point of a gravitational field to produce the Einstein deflection, is the ratio of the energy of a constant-mass particle fallen there from infinity to the energy of the same particle moving with the speed of light; but it is not permissible to say that the solar gravitational field acts like a lens, for it has no focal length. If the sun were backed by a nebula or any luminous area, the light grazing the rim all round would be brought to a focus at a place seventeen times the distance of Neptune, while light from any larger circle would focus still further off in proportion to the area of the circle. So from a uniformly luminous area there would result a focal line of constant brightness. The moon is, unfortunately, impotent to make an annular eclipse interesting.

Access optionsAccess options

Rent or Buy article

Get time limited or full article access on ReadCube.


All prices are NET prices.

Author information


  1. Edgbaston, Birmingham, November 30.



  1. Search for OLIVER J. LODGE in:

About this article

Publication history




Further reading


By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.