2 2 0 D O C . 2 1 9 A N E W U N I F I E D F I E L D T H E O R Y The case when an electromagnetic field is completely lacking is characterized by the vanishing of the φμ. In that case, (7) agrees with the equation used thus far in general theory of relativity, in the first order quantities (R  is the singly contracted Riemannian tensor). This proves that our new theory correctly reproduces the law of the pure gravitational field to first order. By differentiating (2a) with respect to x  , one obtains the following equation, taking into account the equation found from (5) by applying contractions in α and β: … . (8) Considering that the left-hand side L  of (7) obeys the identity , it follows from (7) that , or … . (9) Equations (8) and (9) together are, as is well known, equivalent to the Maxwell equations in vacuum. The new theory thus yields the Maxwell equations in first ap- proximation, as well. The separation of the gravitational field and the electromagnetic field appears, however, to be artificial in this theory. It is also clear that equations (5) contain more information than equations (7), (8), and (9) all together. It is furthermore no- table that according to this theory, the electric field does not enter into the field equations quadratically. Note added in correction.[9] One obtains quite similar results by starting from the Hamilton function . There is thus for the time being a degree of uncertainty in the choice of H. R  0 =  x   0 = [p. 227]  x  L  1 2 --   L  –    0 = 2  x  2   x  x  2   x   x       – + 0 = 2  x  2  0 = H hg  g  g        =