No one would wish to strain at a gnat. If the relativist finds it convenient to make the time-axes of his four-dimensional medium the pure imaginary direction by writing, t=τ√(-1) that would appear to be a matter of indifference, so long as for each coordinate a single line or axis still suffices to indicate the values that x, y, z, and τ can bear. But the matter becomes complicated as soon as we project in oblique directions. Thus take the equations of the “restricted” relativity theory