7 8 D O C . 9 6 A U G U S T 1 9 1 9 Lorentz transformation. It would be different if the radii were considered material, but not the tangential connections of their endpoints. What you say about the measuring rods and clocks placed on the periphery is completely untenable. An unjustifiable transferral of results of the special theory of relativity to accelerated systems (relative to the inertial system) is involved there. Freundlich and Schlick are definitely right here. By your manner of deduction, one could just as well conclude that every light ray must propagate along a straight line relative to an arbitrarily rotating system, etc. Your misunder- standing is very fundamental. I would have much more to say, but face-to-face ar- gument and counterargument are much easier. With best regards, yours, Einstein. 96. From Jean Perrin Paris, 28 August 1919 My dear Einstein, First of all, I would like to tell you that it was a great comfort for everyone here who admired and liked you to learn from our friend Pierre Weiss that since the beginning of the great ordeal and throughout its entire duration you always knew where to look for justice. We shall have a lengthier chat about that someday and, in recollecting our old conversations, I cherish the hope that we should have very closely related con- ceptions of the Ideal towards which Humanity should strive. From the point of view of science, Weiss tells me that you have achieved some very great things, and I am not surprised. I would be very pleased if you could send me (Sorbonne, Paris) a few [offprints]. Without drawing any comparison, toward the end of the war I also managed to write up the lecture I had given in Zurich (Fluorescence, Luminescence), delving somewhat deeper. Above all, I developed an idea that I had already introduced to you (around 1911, I believe, or 1912???) [on] chemical reactions. (You then doubted that any mono- molecular decomposition would take place in gaseous media without a catalyst— but I believe the objection can be removed.) I would be gratified if you read this paper carefully (Matière et Lumière). There you will find, in particular, a theory of radioactivity that, provided it is accurate, would be of importance.