The critical equation in Prof. Einstein’s relativity theory of gravitation is given in the form ( du / dϕ ) 2 + u2 = c2 — 1/ h2 + 2 mu / h2 + 2 mu3 , where m is the mass of the sun, u is the reciprocal of the distance of the moving body from the sun, h2 = ma (1— e2 ), c2 — 1 = — m / a , a is the “major semi-axis of the orbit,” the units being astronomical, and e is the “excentricity” of the orbit. The foregoing equation can be integrated exactly, the functions involved being elliptic and not circular; and the approximations for the solar system are easily obtained, because the modulus of the elliptic functions is small.