On the models of gravitational fields

Modelling of the gravitational field is discussed within the framework of Einstein's theory. Modelling is defined as the mapping whereby the geodesic lines (the path of test bodies) go into the family of curves given by the equation of a test body motion in a model. Different possible ways of modelling are singled out — namely, the complete, selective, and approximate-selective ones. The theory is applied to the solar gravitational field.Presented at the International Conference on Gravitation and Relativity, Copenhagen, July 1971. Professor Petrov died in the Summer of 1972. He was one of the members of the International Committee on GRG and founder of the Journal on GRG. We are happy to publish this contribution of his and shall respectfully keep him in our memory. (The Editor.)