at which we arrive in the [second section], using as our basis the two fundamental postulates. The new functions
that now occur may be interpreted as the potentials of the gravitational field, if we take our stand on the hypothesis of equivalence. To calculate the quantities from the factors determining the gravitational field, namely, matter and energy, it immediately suggests itself to us to assume a system of differential equations of the second order, that are built up analogously to Poisson's differential equation for the Newtonian gravitational potential. These differential equations, together with the fundamental law of motion, represent the fundamental equations of the new mechanics and the theory of gravitation.
Since the new theory uses the generalized curvilinear co-ordinates
,
,
,