December 6, 1943

Dr. W. T. Astbury

Textile Physics Laboratory

The University

Leeds, 2

England

Dear Astbury:

Both Dr. Shaffer and I have been so busy during the last two or three years that we have not succeeded in getting our paper on the use of punched card machines in x-ray and electron diffraction calculations ready for publication; I am accordingly writing this letter in answer to your letter of November 8, instead of sending the reprints which you requested. We hope to finish preparing a description of this work for publication before long.

The x-ray calculations and electron diffraction calculations are made with use of a sorter and an alphabetic tabulator. The eighty columns of the alphabetic tabulator are divided into twelve fields of six columns each and a field of eight columns which is used for the description of the calculation. The twelve fields of six columns each are used for carrying out simultaneous summations for twelve values of the angle argument. Our x-ray Fourier series punched cards come in packs of eleven cards, representing 126 values of the argument, covering one-quarter of a revolution at intervals of 0.002 revolutions. Sine and cosine functions up to the frequency of 36 are included in the table, and amplitudes of plus and minus 500, 400, 300, 200, 100, 50, 40, 30, 20, 10, 5, 4, 3, 2, 1, permitting, by combining several packs of cards, any integral amplitude from -1000 to +1000 for sine and cosine functions of any frequency within the range covered. The evaluation of a Fourier sum is made by packing out the appropriate packs of cards, rearranging them in the sorter in such a way that all of the first cards are together, all of the second cards, etc., and then passing them through the alphabetic tabulator, which sums the twelve columns, prints the twelve answers, resets itself to zero, and proceeds with the similar treatment of the next twelve values. A calculation is good to about four significant figures. There is a great saving of time over any other method of calculation with which we are acquainted.

The great labor involved in this work was that of preparing the original master set of punched cards. I suggest that if you find it possible to make use of this method it would be far better for you to obtain a duplicate set of our cards than to do the work ab initio.

We also have an extensive file of cards for use in electron diffraction calculations. The punched card machines have been found of further use in the solution of simultaneous equations.

We would be glad to help you in any way that we can.

With best regards, I am

Sincerely yours,

Linus Pauling

LP:jr

December 6, 1943

Dear Dad,

I was very happy to receive your letter and the enclosure. Thank you very much. What with Christmas shopping to do I'm going to need all I can get.

I have very bad news. I washed out of air crew training on the psychological interview. The psychiatrist decided that I was subject to too much nervous tension. This rejection was awfully disappointing to me. Apparently my other test were all right, although I'm not certain yet. I asked the flight surgeon, and he said that I could reapply for cadet training after I have proved myself in combat. Armoror's [sic] school takes nine weeks, aerial gunnery six weeks, so if things move along I can see action inside of a year. The sooner the better.

Meanwhile, training proceeds as usual. Everyday some of the boys report to sign questionnaires and get their folders, and then they are happy because they are eligible for shipment to college. About fifteen of the original hundred of our group have washed already. Undoubtedly more will, since those that washed are deficient medically, and we had many stiff mental aptitude test that will show up faults.

The psychomotor test was extremely interesting and a great deal of fun. All information concerning it is supposedly confidential, but I think you ought to hear about it.

The first test was a board with rows of square holes in it and square pegs with round heads.

They are turned 180 as rapidly as possible.

The next test was a wheel with a spot in it. The wheel revolved, as we held a pencil to the spot and pressed one of two buttons with the other hand as two lights flashed.

The third was a little machine with a wheel that contained a button that moved in a slot. A contact, operated by the handles shown, moved around over the wheel.

The next was a board with lights. As combinations of lights flashed on, we pushed one of four switches.

The fifth was a machine with rudder bar and joy sticks and a board with pairs of lights. A combination of green lights would flash on, and we matched the red one up with the controls.

The last test was a small plane held in place by springs which were attached to a rudder bar. Our problem was to keep the plane balanced on a target.

This psychomotor was like a penny arcade, and we enjoyed ourselves doing it. Give my love to mom and the kids

Love,

Linus

P.S. I'm sending you the last two editions of the post paper.