Scientists know that research merely discloses parts of the infinite unknown. Paradoxically, the enticing, helpful "unknown" increases as men continue to subtract from it. Progress in every line of experimental science follows the same law. The apparently narrow path gradually expands into unlimited, unexplored territory.

Annual Report of the Board of Regents of the Smithsonian Institution, 1924, The Vacuum — There's Something in It (p. 194), Government Printing Office. Washington, D.C. 1925