It's a book about the big volcanic eruption at Krakatoa. This was a popular book back in the day; a lot of folks talked about it. Thus, instead of learning new things by reading this book, I mostly was just nodding my head and thinking "oh yeah, I think someone told me something about that." There are places where I could have learned things, but I just skimmed. There was a lot of detail about continental drift and geology and subduction and all that. But I'm pretty sure I've read detailed descriptions of this before and it's gone in one ear and out the other. In one brain lobe and out the other? Uhm, I've forgotten it and figured I'd forget it again and so just skimmed these parts.
One piece of trivia I learned (though maybe folks told me this and I forgot? anyhow…): the air-pressure wave from the eruption went around the Earth several times. You could hear the sound a fraction of the way around, but not all the way around. But scientists looking at recordings on their then-newfangled recording barometers (and comparing notes with fellow scientists around the globe) could "see" that the wave had gone around a few times. It's not intuitive: I'd assume that noise would drown out that signal. But like a Marshall Islands navigator picking out the water wave reflecting off of some far-off island, the barometer could still detect that air-wave going around.