THE UNIVERSITY,
GLASGOW, W.2.
  TEL KELVIN 2231

13th December, 1951.

Dr. W, Gochran,
Crystallographic Laboratory,
Cavendish Laboratory,
Cambridge.

Dear Dr. Cochran and Crick,

I thank you for your letter of 12th December.

        I started a numerZca1 calculation for the Pauling
hel9x some time ago by preparing a few graphs of Cn functions,
intending to try them on the data of Mrs. Hodgkin for insulin.
However, I did not get very far beyond this stage, so that if
you are going ahead with numerical calculations, Pt would be
a pity to duplS_cate them here.

       I think that a graphical method might be quite
adequate, the evaluation being done by superimposing over the
C, graph a sheet of tracjng paper with a properly oriented
square net drawn on to it, the scale of the net depending on r
and its orientation on the z co-ordinate of the,atom.   In thSs
way the values of Cn are evaluated on points of a standard
square net in reciprocal space, and contributSonsfrom different
atoms are thus rapidly added at each point of the net.

       The Sn values can be obtained from the Cn
graphs by providing a separate angular scale, say in red.
I am sending you a part of my Co graph, 9n case you have not
already plotted one;
rapid.         the evaluation is, as you will see, very
    Do you think a graph like this should be included in
the paper,
results?  or in some subsequent papers dealing with numerical

Yours sincerely,

7 ?&I.. --=A
                  -
  V. Vand.

Encl.
--