Appleton's dictionary of machines, mechanics, engine-work, and engineering (1869)
New York, Appleton · leaf 617
easily seen by examining Fig. 8297, in which Qg represents the lens, A its centre, F theprincipal focus, bF and V F the radius of the flame; then is the angle b Ab equal to the maximum divergence of the lens. Sin b A F = ——, = sin V A F = ..— ; and twice b A F = the whole A b local distance… … —.__ tt —-v On the subject of the illuminating power of the lenses, it seems enough to say that the same genera)principle regulates the estimate as in reflectors. Owing to the square form of the lens, however, thereis a greater difficulty in finding a mean focal distance whereby to correct our…
Mechanical engineering
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