1. R. S. Uhrbrock , Science 128 , 747 ( 1958 ).
2. W. Shockley Proc. I.R.E. (Inst. Radio Engrs.) 45 279 (1957).
3. The designation government includes laboratories operated by a national government or 1278 operated for it by universities or industrial contractors. Foreign "institutes of physics" were classed as academic.
4. In cases where the names of laboratories of more than one category appeared in a by-line prorated fractions were assigned to the number of communications from each category for that value of N. In Fig. 1 the sesulting numbers were rounded to the closest integer above.
5. H. N. V. Temperley , Science 124 , 355 ( 1956 ).