Elements of natural philosophy (Volume 2-3) (1850)
Bartlett, W. H. C. (William Holms Chambers), 1804-1893 · New York : Barnes · leaf 225
all, and that 2, theversed-sine of the angle d, included between the axis andthe radius drawn to the point of incidence of the extremerays of the pencil, is so small, that all the products ofwhich it is a factor may be neglected. If, however, z beretained, and Equation (18) be solved with reference… … z is the versed-sine, be made tovary from zeroto any magni-tude sufficient toembrace the ex-terior rays of anydefinite pencil, it is obvious that fz\ must have an infinite number ofvalues, and that each value will give the focus for thoserays only which make up the surface of a cone and areincident…
Mechanics · Acoustics · Optics
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