Billington, D. S. & Crawford, J. H., Jr. Solid State Division Semiannual Progress Report for Period Ending August 30, 1956, report, December 17, 1956; (https://digital.library.unt.edu/ark:/67531/metadc100308/m1/1/: accessed April 25, 2024), University of North Texas Libraries, UNT Digital Library, digital.library.unt.edu; .