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It was on March 10, 1876 that Alexander Graham Bell made the first successful telephone call. "'Mr. Watson--come here--I want to see you," he said to his assistant, who was in the next room. Bell recorded those early telephone experiments in his lab notebooks from the time, as he did with countless other experiments and ideas.

The books are a priceless treasure of an incredibly fertile mind working through one of the most exciting periods of technological innovation in the history of the world. The sketches, though, are more than just dry recordings of physical principles. Bell's drawings are expressive in ways that few technical sketches are. Little flourishes and annotations make paging through his drawings a delight.

Sadly, his handwriting doesn't have the same precision as his drawings. You'll probably have as tough a time as I did making out his intentions. Nonetheless, we can appreciate Bell's genius even without the full explanations of what he was thinking.

Bell's notebooks have been preserved by the Library of Congress, which digitized them, turning them into one of the Internet's real treasures. We present a selection of the best images here.