1. Start with what you already have: to uncover references to primary sources
2. Use the library catalogue to find primary sources
3. Browse or search reliable online collections, such as the ones in this research guide:
• Sources for Historical Scientific Publications
• Historical Newspapers & Periodicals
• Databases of Primary Source Collections (ex. letters, diaries, etc)
• Digital Collections & Online Archives 
  

For a refresher on the difference between primary sources and secondary sources, click here.

The following may refer you to good primary sources on your topic. 

• class notes
• course readings
• bibliographies/footnotes/endnotes of your textbook, journal articles, or other secondary sources
• historical encyclopedias

They can also help you identify relevant historical figures authors, or keywords for searching library databases. 

For example, in Tim Lewens' book Darwin (shown below), he discusses Darwin's remarks on a "moral sense". In this context, Tim Lewens' book is a secondary source, and his reference (Darwin's Descent of Man) is the primary source. If you wanted to analyze for yourself Darwin's thoughts on morality, you would know now to check out  Lewens' references, find this particular edition of Descent of Man in the library catalogue and read around page 120. 

Remember when you're reading secondary sources to look for relevant keywords and thinkers. If I was interested in Darwin and morality, I would make sure to jot down ethics, moral sense, biologicized as important keywords to search and EO Wilson as an important person to read up on. 

Combine keywords for different kinds of primary sources with keywords for your topic to find them in the library catalogue.

Primary source keywords

Examples:

Darwin correspondence

evolution early works

Eugenics personal narratives