Appleton's dictionary of machines, mechanics, engine-work, and engineering : illustrated with four thousand engravings on wood ; in two volumes (1873)
D. Appleton and Company · New York : D. Appleton and Co. · leaf 616
The central disk of the lens, which is employed in lights of the first order, and whose focal distance is 920 millimetres, or 3622 inches, is about 11 inches in diameter; and the annular rings which surround •t gradually decrease in breadth, as they recede from the axis, from 2J to IJ inches. The…
Mechanical engineering · Mechanics · Engineering
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