In the follovving a method is proposed to determine the mean coefficient of interstellar absorption and the mean extinction from the observed spectroscopic parallazes, the radial velocity and the proper moti- ons. The distribution $ (x, y, z/S) is assumed to be constant in the immedi- ate surroundings of the sun. This is a reasonable assumption. Therefore the velocity Iaw must be a constant along any axis. independent of its orienta- tion. In different areas of the sky it is cor.venient to adopt as axis the radi- us vector and the direetion perpendieular to and tangent to the cireles »and S The equations of motion containing a are derived. From these the nume- rical values of a can easily be derived.