A primary source is a document or physical object which was written or created during the time under study. They are often unpublished works. Some types of primary sources in the history of physics include:
Primary sources are distinguished from secondary sources, which cite, comment on, or build upon primary sources.
Some primary materials have been digitized by libraries, museums, and other organizations to make them more accessible. Digital collections of primary materials may be found by using a web search engine. Some examples of sites containing such collections are: