As we have noted, once the irrelevance of the ether drift is admitted and the equations of electromagnetics accepted as accurate, we are led to those space and time transformations known as the Einstein-Lorentz transformations. When we assert that duration might just as well have been defined in terms of moving bodies or sound transmissions (under ideal conditions of observation), our statement is equivalent to asserting that the Lorentz-Einstein transformations, though obtained from a study of electromagnetic and optical phenomena, are yet of universal applicability to all manner of phenomena. Here the critic may object that this is a gratuitous assumption. Maybe it is, but we must understand that were its validity to be contested, were the classical transformations to hold for mechanics and acoustics, while the Lorentz-Einstein ones were valid for electromagnetic processes, we should be faced with insufferable contradictions. Thus, according to the Lorentz-Einstein transformations, as applied to electromagnetics, a ray of light proceeding in vacuo will pass any two different Galilean observers with the same speed . But according to the classical transformations, as applied to mechanics, a body which is moving with the velocity with respect to one observer will be moving with a different velocity relatively to the second observer. If, then, a body were moving along with the crest of a light wave in the opinion of one observer, it would either outstrip the wave or fall behind it in the opinion of the second observer. A coincidence for one would no longer be a coincidence for the other. Coincidence would thus cease to be absolute, and it is doubtful whether any science could exist, since all unity in nature would be lacking. Furthermore, the coexistence of two conflicting species of space and time transformations appears very improbable when we remember that it is impossible to establish a clear-cut distinction between mechanics and electrodynamics, since matter seems to be in large part an electromagnetic phenomenon. [Pg 185] Hence it is only natural that the scientist should assume that the Einstein-Lorentz transformations, though deduced from electromagnetic or optical processes, should yet hold in all domains of physical science, even in the interior of the atom. It is true that these transformations were obtained from a study of optical and electromagnetic phenomena, not from acoustics or mechanics; but this is merely because experiments as sensitive as those of Michelson and Fizeau could scarcely have been performed with sufficient accuracy had sound waves, nerve excitations or ripples on the water been contemplated. And yet, had Fizeau’s experiment been performed with sound waves, there is every reason to suppose that the curious composition of velocities would have been observed.