APA Citation
Marconi, Guglielmo,. Guglielmo Marconi letter to H.H. McClure, dated Marconi's Wireless Telegraph Company, Limited, Table Head, Glace Bay, near Sydney, Cape Breton, 7 November 1902. Retrieved from https://library.si.edu/digital-library/book/guglielmomarcon00marcl
MLA Citation
Marconi, Guglielmo,. Guglielmo Marconi letter to H.H. McClure, dated Marconi's Wireless Telegraph Company, Limited, Table Head, Glace Bay, near Sydney, Cape Breton, 7 November 1902. https://library.si.edu/digital-library/book/guglielmomarcon00marcl
Chicago
Marconi, Guglielmo,. Guglielmo Marconi letter to H.H. McClure, dated Marconi's Wireless Telegraph Company, Limited, Table Head, Glace Bay, near Sydney, Cape Breton, 7 November 1902. https://library.si.edu/digital-library/book/guglielmomarcon00marcl
Warning: These citations may not always be complete (especially for serials).