The article starts with a general introduction to the problem in modern physics about the constancy of the speed of light for all frames of reference. In the “General Introduction”, besides presenting the used terms and definitions, the fundament of a real solution about all “unexpected” and “inexplicable” results of the experiments related to the measurement of the velocity of light in the time-spatial region “on the Earth surface” is given. The famous “Michelson-Morley” experiment has been carried out in order to determine the change of the speed of light due to the motion of the Earth in its orbit around the Sun. On the base of the known speed of the Earth (approximately 30 km/s) the Michelson’s expectations had been that the displacement of the interference fringes will be different at night and during the day (when the directions of the “ether wind” caused by the movement of the Earth in its orbit around the Sun are opposite),… and will correspond to the calculations made. However, the result has been unexpected - no displacement was fixed. The problem has two reasons. The first is that the speed of light in vacuum depends on the intensity of the gravitational field. The intensity of the gravitational field near the Earth’s surface is dominated by the mass of the Earth and does not change during the revolution of the Earth around the Sun. Therefore, the speed of the electromagnetic radiation (of the light) in vacuum remains constant during the travel of the Earth through space. The second reason is the inappropriate conceptual design used in the construction of Michelson's interferometer. The difference in the speed of light between the two light beams, traveling in two opposite directions on the same arm, is completely compensated when the “two-way light beam interferometer” is used (see the arguments below). That is why, the existing difference of the speed of light due to the rotation of the Earth around its axis in the direction „East-West” and “West-East” (in the reference system related to the Earth's surface) cannot be established. However, that difference is observed at the experiments “One-way measurement of the speed of light” and the experiment “Michelson-Gale-Pearson”. The final conclusion is that the “Michelson-Morley experiment” is actually the primary root cause for the delusion that “the speed of light is the same for all inertial frames of reference”, which is the core of the special theory of relativity.