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 617
9. This will be easily seen by examining Fig. S297, in which Q q represents the lens, A its centre, F theprincipal focus, bF and b F the radius of the flame; then is the angle b Ab equal to the maximiim divergence of the lens. Sin j A F = --^;^ = sin 6 A F = r^—t—tt : and twice 6 A F = the whole A… … On the subject of the illuminating power of the lenses, it seems enough to say that the same generalprinciple 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 tt> correct our estimate of…
Mechanical engineering · Mechanics · Engineering
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![An illustration from Nicolai Copernici Torinensis De reuolutionibus orbium coelestium, libri VI : Habes in hoc opere iam recens nato, & aedito, studiose lector, motus stellarum, tam fixarum, quàm erraticarum, cum ex ueteribus, tum etiam ex recentibus obseruationibus restitutos: & nouis insuper ac admirabilibus hypothesibus ornatos. Habes etiam tabulas expeditissimas, ex quibus eosdem ad quoduis tempus quàm facillime caculare poteris. Igitur eme, lege, fruere. [Line in Greek] (1543)](https://img.insideoutlibrary.com/img/200/ia-nicolaicopernici00cope-356-247.webp)
