This is the most reliable "legal" source for PDFs. Many libraries have scanned older editions (such as the 1960s–1990s sets) and made them available for free viewing or borrowing. Digital Libraries:

| Aspect | Assessment | |--------|-------------| | | Highly variable – some scans are clear OCR-ready; others have skewed pages, stains, or missing plates. | | Searchability | Most scanned PDFs are image-only (no searchable text). True searchable PDFs require OCR processing. | | File size | A complete 16-volume set can exceed 2–4 GB. Single volumes range from 100–400 MB. | | Navigation | Lacks original print’s tactile ease. Best viewed on tablets or computers with PDF bookmarks if included. | | Legal status | Pre-1964 editions may be public domain in the US; later editions are copyrighted. Downloading unauthorized copies may violate law in your country. |

What you will have is a bespoke, searchable, offline library that smells like history.

The PDF versions usually retain the original high-quality illustrations, maps, and diagrams that made the print version famous. Tips for Searching