huinventors1-4, Exercise 1: The problem and the ball

Model answer:

The problem was that fountain pen ink dries slowly, smudges and blots, whereas the ink used in newspaper printing dries almost at once. But thick, quick-drying ink will not flow through the narrow nib of a fountain pen. Bíró's answer was a tiny ball held in a socket at the tip, rolling against the paper and picking up ink from a reservoir behind it as it turns, so the ink is delivered by the rolling and the thick ink can be used. His brother György, a chemist, is said to have helped with the ink. Details should be checked.