A regular approach looks the speed of gravitation as a speed of weak waves of the metrics. This study realizes a new approach, defining the speed as a speed of travelling waves in the field of gravitational inertial force. D'Alembert's equations of the field show that this speed is equal to the light velocity corrected with gravitational potential. The approach leads to the new experiment to measure the speed of gravitation, which, having "detectors" like as planets and their satellites a base, is not linked to deviation of geodesic lines and quadrupole mass-detectors with its specific technical problems.