In 1885, there were 15 lighthouse districts in the US, and over each served an inspector, who visits every light-station quarterly, and his duties include maintenance of all those aids to navigation in it, the discipline of its personnel and pay to each keeper. When he visits a lighthouse that has a library he takes it away and replaces it (Google books preview). Those traveling lighthouse libraries were carried in heavy-duty, dual-purpose boxes that doubled as small book cases. [more inside]
The Pack Horse Librarian (Photo Gallery) was a welcomed and much anticipated sight in the isolated and hard-to-reach mountains and hollers of Eastern Kentucky between 1935 and 1943. They brought books and magazines, retrieved already-read materials for delivery at another stop on the route, read to residents, took requests, and generally served homes, schools, villages, mining camps, and anywhere there were people who wanted to read. [more inside]
"Learn me to read, book lady.... Please if you learn me, I won't be lonesome any more. I broke my back last year. It wan't mended yet." A look at WPA Travelling Libraries. See also: Free traveling libraries (Wisconsin), Lighthouse libraries (Coastal U.S.), Blue Trunk Medical Libraries (Africa), Bus Libraries (China), a few miscellaneous mobile libraries, and this one from the 16th Century. And yes, there's some YouTube.