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Uh, help? On pages 26-31 of this issue of The American journal of science published in 1881 there's an article on changes in the length of a 4 m zinc bar. Basically, they measured it, heated it, let it return to its starting temperature and measured it again. And there was a 29 mkm difference between the two measurements. I didn't quite understand what they did, and the Fahrenheit degrees didn't help any, but - what's the catch?..