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As many other points as may be desired in the curve NC are found by a Theorem which Mr. Barrow has demonstrated in section 12 of his Lectiones Opticae, though for another purpose. And it is to be noted that a straight line equal in length to this curve can be given.
Now imagining the incident rays as being infinitely near to one another, if we consider two of them, as RG, TF, and draw GQ perpendicular to RG, and if we suppose the curve FS which intersects GM at P to have been described by evolution from the curve NC, beginning at F, as far as which the thread is supposed to extend, we may assume the small piece FP as a straight line perpendicular to the ray GM, and similarly the arc GF as a straight line.
The Navy Department called for the big flying boat; and the NC type was evolved, which, equipped with four Liberty Motors, crossed the Atlantic after the close of the war. The World War, of course, brought about the magical development of all kinds of air craft. Necessity not only mothered invention but forced it to cover a normal half century of progress in four years.
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