1. Lens-Like Action of a Star by the Deviation of Light in the Gravitational Field
2. Schneider P., Ehlers J., Falco E. E., Gravitational Lenses (Springer, Berlin, 1992).
3. Eddington A. S., Space, Time and Gravitation (Cambridge Univ. Press, Cambridge, 1920), pp. 133-135 and 208-209.
4. Chwolson O., Astron. Nachr. 221, 329 (1924).
5. Einstein may well have been aware of Chwolson's short note (4) because a short note of his own (a response to W. Anderson on the problem of the theory of electron gases) appeared in the same issue of the same journal and was in fact printed on the very same page as Chwolson's note.