Einstein's Second Letter to Roosevelt

The crucial letter that started the nuclear arms race

March 7, 1940

I wish to draw your attention to the development which has taken place since the conference that was arranged through your good offices in October last year between scientists engaged in this work and governmental representatives.

Last year, when I realized that results of national importance might arise out of research on uranium, I thought it my duty to inform the administration of this possibility. You will perhaps remember that in the letter which I addressed to the President I also mentioned the fact that C. F. von Weizsäcker, son of the German Undersecretary of State, was collaborating with a group of chemists working upon uranium at one of the Kaiser Wilhelm Institutes - namely, the Institute of Chemistry.

Since the outbreak of the war, interest in uranium has intensified in Germany. I have now learned that research there is carried out in great secrecy and that it has been extended to another of the Kaiser Wilhelm Institutes, the Institute of Physics. The latter has been taken over by the government and a group of physicists, under the leadership of C. F. von Weizsäcker, who is now working there on uranium in collaboration with the Institute of Chemistry. The former director was sent away on leave of absence, apparently for the duration of the war.

Should you think it advisable to relay this information to the President, please consider yourself free to do so. Will you be kind enough to let me know if you are taking action in this direction?

Dr. Szilard has shown me the manuscript which he is sending to the Physics Review in which he describes in detail a method of setting up a chain reaction in uranium. The papers will appear in print unless they are held up, and the question arises whether something ought to be done to withhold publication.

I have discussed with professor Wigner of Princeton University the situation in the light of the information available. Dr. Szilard will let you have a memorandum informing you of the progress made since October last year so that you will be able to take such action as you think in the circumstances advisable. You will see that the line he has pursued is different and apparently more promising than the line pursued by M. Joliot in France, about whose work you may have seen reports in the papers.

Source:

Ronald W. Clark. Einstein: The Life and Times. New York: Avon Books, 1970: 681.