1. Bell's Experimental Notebook, 10 March 1876. Alexander Graham Bell Family Papers, Manuscript Division, Library of Congress.
2. Alexander Graham Bell Speaking on the Phone, 1892. Reproduction Number LC-G9-Z2-28, 608-B. Gilbert H. Grosvenor Collection, Prints and Photographs Division, Library of Congress.
3. [Samuel F. B. Morse, head-and-shoulders portrait, facing front]. Created between 1844 and 1860. Produced by Mathew Brady's studio. Reproduction Number LC-USZ62-110084 DLC (b&w film copy neg. post-1992). Daguerreotype Collection, Prints and Photographs Division, Library of Congress.
4. First Telegraphic Message, 24 May 1844. The Papers of Samuel Finley Breese Morse, Manuscript Division, Library of Congress.