Published in 1908, this isn't a novel with characters, but a scientific argument presented like a story. The 'plot' follows astronomer Pierre Puiseux as he gathers all the known evidence about the Moon—its shape, the way it wobbles in orbit, the patterns of its craters and plains—and uses it to answer a fundamental question: what's inside it?

The Story

Puiseux acts as a cosmic detective. He starts with the Moon's exterior, meticulously describing its surface features as seen through telescopes. Then, he moves inward. By analyzing how the Moon's gravity affects Earth's tides and its own motion, he makes deductions about its density and structure. The central tension is between two ideas: a Moon that is uniformly solid and cold versus one that might have, or once had, a differentiated interior with layers, perhaps even a core. He weighs each piece of evidence, building a compelling case for the Moon's internal nature based purely on observation and physics.

Why You Should Read It

What's captivating is the human element. You're seeing the limits of knowledge in 1908 and the clever ways scientists pushed past them. Puiseux's reasoning is clear and patient. You feel his curiosity as he connects dots between lunar libration, surface geology, and planetary formation. It's a powerful reminder of how much we can learn just by looking carefully and thinking deeply. Reading his conclusions, knowing what we know now from the Apollo missions, adds a wonderful layer of historical irony and respect.

Final Verdict

This book is perfect for anyone who loves astronomy, history of science, or quiet, thoughtful nonfiction. It's not a light read, but it's not overly technical either. Think of it as a time capsule of scientific thinking. If you enjoy seeing how great puzzles were solved with simple tools, or if you just love the Moon and want to understand how our view of it has evolved, you'll find this deeply rewarding. It's for the curious mind that appreciates a good intellectual journey.