Starting about 1920,
Popular Science turned into a glorious magazine with all kinds of fantastical cover illustrations, and articles which breathlessly told us about the wonders soon to arrive (many of which have failed to ever show up). This all ended sometime in the late 1960s, with only occassional flashes of the old brilliance showing up. Those of us fascinated by the old issues have hunted them in second hand shops and eBay.
Now, it turns out, Google's put all the back issues online. Sadly, you can't download any of the old issues, and searching through them is a bit hit or miss, but there's still plenty of fascinating stuff to keep you occupied for hours, clicking through the old issues.