## 7 Conclusions  
If in the STR and STE kinematics a light signal is used to synchronize the clocks, then the light clock is automatically introduced in these theories as a time standard. In other words, STR and STE are theories in which time is measured by the light clock. These are theories that describe the practical aspects of using such clocks. Therefore, time dilation occurs in these theories. The paper explains the phenomenon of time dilation. Time dilation is a natural property of the light clock. The paper has shown that the time dilation occurring in the relativistic theories of Special Theory of Relativity (STR) and Special Theories of Ether (STE) is identical to the one that results from the operation of the light clock. The paper explains why STR transformation (Lorentz transformation) and STE transformations cease to operate when the speed of inertial systems reaches the value \(c\) that occurs in these transformations. The presented analysis shows that speed \(c\) occurring in transformations is not a speed limit in the physical sense but a speed at which the light clock stops operating. In systems moving at velocities \(c\) or above, the light clocks stop measuring time. Therefore, it is not possible to describe the processes taking place in such systems with light clocks. However, from STE and STR not results, that speed \(c\) is physically impassable to exceed. It has been shown that if classical kinematics is introduced to the measurement of time by means of a signal clock, based on a signal with a finite speed, then also in this theory will appear the time dilation phenomenon. In order for the time dilation phenomenon not to occur, the speed of signal used by the clock must be infinite (or equivalent \(v<<c\)). This is how it is in the classical approach to classical kinematics, so there is no time dilatation in it. The existence of the time dilation phenomenon is indirect proof of the existence of a universal frame of reference (ether) in which the light propagates. If atomic clocksare subject to this phenomenon, it results from the fact that perhaps they use in their operation a propagating signal in a distinguished medium (it is possible that it is an electromagnetic signal). Presented analysis shows that one of the ways of testing the movement in relation to ether can be the measurement of time with atomic clocks inclined at different angles to the direction of movement in relation to ether. Perhaps a comparison of time measured with such clocks will enable measurement of the speed in relation to ether if longitudinal or transverse contraction does not compensate for the differences in time dilatation in an ideal way. The paper [1] shows that [PERSON]'s and [PERSON]'s experiments are not able to detect movement with respect to ether in case of an infinite number of different kinematics with ether. In the case of these kinematics, the measurement with atomic clocks will not be effective either. However, if longitudinal or transverse contraction does not compensate for the differences in time dilatation in an ideal way, then the measurement with atomic clocks can be more effective due to the very high accuracy of modern atomic clocks. Time is what we measure by some kind of physical process. Only cyclic processes, e.g., seasons, pendulum fluctuations (pendulum clocks), quartz crystal vibrations (quartz clocks), atomic oscillations (atomic clocks), or even the reigning periods of successive emperors, are of practical importance. Different physical processes have different sensitivity to changing environmental conditions. Therefore, different ways of measuring time have different individual properties. For example, the time lapse measured by a pendulum clock is sensitive to gravity field intensity, while the time lapse measured by biological cycles is sensitive to different conditions determining life expectancy.