I did not indicate the transformation which suits best. That was done by Poincaré and then by Mr. Einstein and Minkowski. [...] Because I had not thought of the direct way which led there, and because I had the idea that there is an essential difference between systems x, y, z, t and x′, y′, z′, t′. In one we use – such was my thought – coordinate axes which have a fixed position in the aether and which we can call "true" time; in the other system, on the contrary, we would deal with simple auxiliary quantities whose introduction is only a mathematical artifice. [...] I did not establish the principle of relativity as rigorously and universally true. Poincaré, on the contrary, obtained a perfect invariance of the equations of electrodynamics, and he formulated the "postulate of relativity", terms which he was the first to employ. [...] Let us add that by correcting the imperfections of my work he never reproached me for them.