When historians talk about "primary sources", they mean a letter or a diary entry. A telegram, a newspaper report from the day of an event like 9/11 - - something that was written by someone who was present at an event, or is describing their own experiences.
When scientists talk about "primary sources" we mean something completely different. A primary scientific source is essentially a formal research report or lab report. It describes in careful detail - - described so carefully, in fact, that it can be reproduced by others - - the exact steps and procedures that the scientists followed to get the research results they are writing about.
