Slashdot has the good news, that Popular Science magazine has scanned every issue they have ever produced. They are making them available through Google Books, embedded within their own web site. There are the occasional unobtrusive Google ads overlaid on the page scans as you search and flip through, meaning that PopSci and Google no doubt expect some decent ad traffic to sustain the otherwise free offering.
The scan quality is pretty good though I found the lack of a way to browse the issues by date a bit annoying. However, with over a century of content, search is probably going to be a way more useful means of locating articles of interest.