Six lectures on light : delivered in America in 1872-1878 (1886)
Tyndall, John, 1820-1893 · New York : D. Appleton · leaf 151
Let us push our test still further. By means of anendless screw, the crystal can be turned ninety degreesround. The black image, as I turn, becomes gradually Fia. 32.
Light
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