Why is Professor Lidenbrock excited when he returns from the bookshop in A Journey to the Centre of the Earth?

Professor Lidenbrock is incredibly excited over a rare book he's just bought from Hevelin's book shop. However, his nephew, Axel, can't see what all the fuss is about; to him, the yellowish old book with the faded tassel dangling from it doesn't look like anything special.
But to the good professor, it's more than a book; it's a treasure. This weighty tome is a 700-year-old book called Heims Kringla by Snorre Turleson, the famous 12th century Icelandic author. It's a chronicle of the Norwegian princes who reigned in Iceland.
Despite his uncle's evident enthusiasm, Axel still finds it hard to get excited about an old book. However, unbeknownst to him—and at this stage, to his uncle—the book contains an ancient manuscript written in Icelandic runes which will reveal how to get to the center of the earth.
Axel may not be particularly excited just yet, but thanks to the book, he will in due course embark upon the adventure of a lifetime.