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 (Communicated in the meeting of January 30, 1915).

The discussion of some parts of 's theory of gravitation may perhaps gain in simplicity and clearness, if we base it on a principle similar to that of, so much so indeed that 's name may properly be connected with it. Now that we are in possession of 's theory we can easily find how this variation principle must be formulated for systems of different nature and also for the gravitation field itself.

Motion of a material point.

§ 1. Let a material point move under the influence of a force with the components $$K_{1},K_{2},K_{3}$$. Let us vary every position $$x,y,z$$