This miniature book was meant to be worn like a holstered Blackberry. Those two holes across the top were for the string that would attach to one's girdle or belt. The book provided the Psalms in English, courtesy of translator John Croke. It measures 1.6 inches by 1.2 inches.
The illustration of King Henry VIII is the main decoration on this British Library artifact from around 1540.
Girdle books, as these miniature tomes were known, are the subject of ongoing scholarly interest. Margit Smith of the University of San Diego and Jim Bloxam of Cambridge University Library published a great review of the research on girdle books in The International Journal of the Book. In it, they note that the impulses underlying their creation are similar to the ones driving today's mobile world:
Girdle books in their various styles combine in one ingenious design a handy way to have a book ready for use, to store it and to protect it. To that end the basic concept and development underlying the medieval girdle book are not far removed from 20th century devices such as palm pilots, electronic books and laptops, all of which stress ease of access, handy format and ready availability. Though the girdle book is practically unknown today, the principles that lead to its development are very contemporary; making the books not as alien as they may seem.
Despite widespread depictions and accounts of girdle book's existence through the second half of the second millennium, only a couple dozen remain in existence, according to Smith and Bloxam.
The Atlantic has tackled the topic of girdle books before, such as in this 1888 history of children's books by Caroline Hewins, a Connecticut librarian. She connected them up to the history of other kinds of mobile learning aids, hornbooks and battledores.
Children had all this time been learning their letters, not exactly from books, but from "hornbooks" and "battledores," the invention of some thrifty and saving person in the days when books were dear. A hornbook of 1570, and another on whose back is a portrait of Charles I. in armor, have only a single leaf, with the alphabet, large and small, the Lord's prayer, and monosyllables. At the top of the older one is a large cross, — the "Christ-cross," from which the alphabet is often called the crisscross row, — and below are the Roman numerals. There is a piece of transparent horn in front, to keep the paper from wet fingers, and the whole is set in a wooden frame with a handle. This handle has sometimes a hole for a string, to sling the book to the scholar's girdle. It is thought that leaden plates were sometimes used for the same purpose, as moulds for them still exist. The battledore, or first book for children, a later substitute for the hornbook, was printed on a card, and contained the alphabet and simple combinations of letters.
Here's an example of a battledore that you can buy a reproduction of at the "Plimoth Plantation."
The point is, I think, that what can be made mobile will be made mobile. And in 2014, I think we're going to find out that almost everything can be made mobile.