The Drummond light, or calcium light as it was also called, was based on a phenomenon that had been known about for a long time—that if you took a lump of lime or magnesia and burned it in a really hot flame, it would glow with an intense white light. Using a flame made from a rich blend of oxygen and alcohol, Gurney could heat a ball of lime no bigger than a child’s marble so efficiently that its light could be seen sixty miles away. The device was successfully put to use in lighthouses, but it was also taken up by theaters. The light not only was perfect and steady but also could be focused
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