Tyndall, John, 1820-1893 · London : Longmans, Green · leaf 452
w^ ^^^W %% ^ Fig. 199. 3 : 4. … which I am indebted to its eminent inventor, may find aplace here, a is a steel rod polished at its upper end soas to reflect a point of light; this rod moves in a ball 430 LECTURE IX. and socket joint at b, so that it may assume any position.Its lower end is connected with two arms c and d,…
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