The pocket book
It is no completely accurate definition for pocket books. It generally refers that the margin is less than 32 size and the pages is roughly no more than 10. The rise of the earliest pocket book can be traced back to the “penguin books” published in July 1935, in London. The series of the books are sold more than 2500 copies, and it gains a huge success. From now on pocket books are popular in the world and started a "paper leather book revolution". It has a profound impact on the publishing industry of Europe and the US, and it is even ranged as human invention, human adventure and unusual event in 20th century with the American invention Kodak color film.