Langstroth on the Hive and the Honey-Bee by L. L. Langstroth

Langstroth revolutionized the beekeeping industry by using bee space in his top opened hive. In the summer of 1851 he found that, by leaving an even, approximately bee-sized space between the top of the frames holding the honeycomb and the flat coverboard lying above, he was able to quite easily remove the latter, which was normally well cemented to the frames with propolis making separation hard to achieve. Later he had the idea to use this discovery to make the frames themselves easily removable