Entire Popular Science archive available online

PopSci, the web-wing of Popular Science magazine, has scanned its entire 137-year archive and put it online for you to read, absolutely free. The archive, made available in partnership with Google Books, even has the original period advertisements.

(Wired Magazine)

Here's the link to Google Books: Popular Mechanics

Additionally, the magazine regularly collects and presents articles from its early archives:
4 Stories from Popular Mechanics' Archives