20 April 1953

Professor Max Delbruck

California Institute of Technology

Pasadena, California

Dear Max:

I received your letter, to Harry Weaver, this morning, and immediately telephoned him.

He had not seen your letter yet, but after I told him what you had said, and what my opinion was, he said that he would bring Watson over for the Virus Symposium.

He suggested that they might save money by having Watson stay here through the summer, instead of returning to England. I pointed out that the work that Watson is doing in collaboration with Crick is very important, and that it might well be important enough to justify sending him back to Cambridge, even for the period of two months. I judge that he agreed to do that, if necessary.

I was very deeply impressed by the Watson-Crick structure, I do not know whether you know what put Corey and me off on the wrong track. The x-ray photographs that we had, which had been made by Dr. Rich, and which are essentially identical with those obtained some years ago by Astbury and Bell, are really the superposition of two patterns, due to two different modifications of sodium thymonucloates. This had been discovered a year or more ago by the King's College people, but they had not announced it, and I did not know that this was so. Corey and I had tried to find the structure that accounted for one of the principal features of one pattern, and simultaneously for one of the principal features of the second pattern, Watson and Crick saw the x-ray photographs made in King's College a couple of months ago, when they attended a seminar there, and they immediately began work on the problem. The King's College people had already derived one conclusion from the photographs, as to the nature of the helical structure. Watson and Crick amplified this by the idea of complementariness between purine and pyrimidine residues, and formulated

Professor Max Delbruck 20 April 1953

their structure. While there is still a chance that their stricture is wrong, I think that it is highly probable that it is right. It has very important implications, as you mention. It think that it is the most significant step forward that has been taken for a long time.

Cordially yours,

Linus Pauling

LP:bfs

cc: Professor Robert B. Corey