the Twenty-One Balloons
I just read the book Twenty-One Balloons, The (PMC) 
by William Pene du Bois.
What a fantastic little read. Professor Sherman is an older retired school teacher who embarks on a year-long balloon trip from San Francisco over the Pacific. Unfortunately it turns into a rather interesting adventure that ends with a crash into the Atlantic ocean just a month later. There are balloons, inventions, explorer societies, diamonds, and the great explosion at Krakatoa island. A good read from a Newberry Medal winner.