If you are looking for specific versions to read without the hassle of multi-part archives:
The file is the first part of a split archive, likely containing digital scans or LaTeX source files for either Isaac Newton's Philosophiae Naturalis Principia Mathematica (1687) or the three-volume landmark logic work by Alfred North Whitehead and Bertrand Russell (1910–1913). 1. How to Open the File Principia Mathematica.7z.001
Depending on the source of your download, the archive likely contains one of the following: If you are looking for specific versions to
A three-volume set focused on the foundations of mathematics and formal logic. Principia Mathematica.7z.001