I hadn't seen this mentioned yet, and I found it very interesting.
With the new google books project to create a digital library, they have made available every back issue of Popular Mechanics from 1905-2005, and Popular Science from 1872-2008. (As well as many other magazines.)
http://books.google.com/books?id=bc8DAAAAMBAJ&source=gbs_summary_s&cad=0#a ll_issues_anchor
http://books.google.com/books?id=F4f6LnrW9NgC&dq=popular+science&source=gb s_summary_s&cad=0#all_issues_anchor