AIR MAIL

Balliol College

Oxford, England

May 17,1948

Dr. Fred J. Ewing

care of Mrs. B. Wulf

Crellin Laboratory

California Institute of Technology

Pasadena 4, California

Dear Fred:

I have decided that I shall have to write to you without having your letter before me. When it arrived I read it, and then tucked it away somewhere— so well that I haven't been able to find it again.

The results that you have got look very good to me. Have I told you that I found it possible to develop a resonating-valance-bond theory of metals, making use of two-electron-bond functions multiplied by suitable Bloch factors, that lead to the same qualitative aspects of the Brillouin zones as the ordinary one-electron molecular-orbital theory, and with the same electron numbers in the Brillouin polyhedra?

I trust that you are going ahead with the evaluation of the electron numbers for important Brillouin zones for various crystals. I am sure that the new results that you mention in your letter plus other similar ones that you probably will have before long will be worth publication.

I would, by the way, like to know what the various interatomic distances are in NaZn13 and other compounds with that structure, in order to check up on the question of the importance of half-bonds, one-third-bonds, etc. Could you make these calculations and send the results to me? You might think it worthwhile to look over the interatomic distances in all of the crystals for which you make Brillouin polyhedron calculations, to see if you find anything new. One troublesome point is, of course, the fact that a difference in hybridization (amount of d character) causes the single bond radii of an atom to be different for its different bonds.

I am not sure that it will be possible for me to send a paper to you for the first issue, that is, a paper of which I am author or co-author. I am very busy, with a number of jobs to get done before leaving for Europe. I believe that I have arranged for two papers from this laboratory to be sent to you, one by Professor Verner Schomaker on the use of punched cards and one by Mr. A. M. Soldate, on the structure of the intermetallic compound FeSi. I have just been talking with Dr. F. J. Ewing about the possibility that he and I could prepare in the near future a brief article on some phase of the structure of metals and intermetallic compounds which would be suitable for the Acta Crystallographica. There is the possibility that we can do this, and if it can be done we shall send you the manuscript as soon as it is ready.

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By the way, I think that we should do something toward improving the nomenclature. For example, coordination number is an awkward end unwieldy expression— we need one short, precise word for this concept. Perhaps ligancy could be used. It would fit in well with ligand and the verb to ligate. We also need some general words to express the bonds between one atom and the surrounding atoms—we now use the word bond to refer both to the electron pair bond that is resonating around among altar-native positions and to the fraction of an electron pair bond that is a portion to a particular position. I have also felt troubled about using the word position in this way—to mean the region between two atoms. If we do introduce any change in nomenclature, it must be very well thought out, and must not involve too great a strain on the memory, or too great a departure from the past.

Our trip to Paris went off well, and after our return (the three children were there with us) Ava Helen and I had a week in Scotland and northern England, during which we combined sight-seeing with lecturing. Now, after the first two weeks of the spring term here at Oxford, the three of us {including Peter) have taken a four-day automobile trip—to Cambridge, Peterborough, Nottingham, Manchester, Chester, Shrewsbury, and back to Oxford.

With best wishes, I am

Sincerely yours,

Linus Pauling:par