Absolute space-time measurements and gravitation.

A method of direct (''absolute'') space-time measurements by means of free trajectories is proposed, and its application to general relativity is discussed. Only the existence and order of the intersections of trajectories are used. Top speed is defined independently at all space-time points and for all pairs of bodies. The ratios of (infinite) oscillation numbers of photons (top-speed particles) provide all the means for geometry: topology, differentiable manifold structure etc. Metric is replaced with these ratios in that a correspondence of affine parameters on different null geodesics can be obtained. So, one is able to define an absolute integration and to construct the Green's functional demanding the field-determining path integral to be finite and expressed solely via oscillation numbers. In particular, the simple geometric structure and immediate physical meaning of the so-called ''tail term'' become evident in connection with Huygens' principle.