What does Axel learn in Chapter 4? How does he respond to this discovery?

After a time he feels that he is almost hallucinating and starts to wave the paper in front of his face to circulate air. When he does so, he notices something about the letters, picking out actual Latin words. To his delight, he sees that he has figured out how to understand the text: simply read the whole thing as one sentence.

After he reads in this manner, his face registers shock. He is astonished by the message and does not want his uncle to see it because Lidenbrock will no doubt pursue the terrible journey that the message details. He decides that all he can do is destroy the document.