Word: convexity
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...present time, the flint is entirely ground and polished on one side, but on the other has yet to undergo corrections for diffraction. Whereas it is now slightly convex on this latter side it will have to be ground flat or even a trifle concave, to bring about the desired result. The crown is already ground and is being put through the process of polishing...
...done as follows: In the first place the curves of the lens are determined by experiments with smaller models, aided, of course, by the maker's long experience. Then an iron disk, large enough to-cover the glass, is made into a concave shape exactly corresponding to the desired convexity of the lens, thus, in reality forming a species of mould. This disk, which by the way is called the "tool," is placed on the glass, and by a simple mechanical device is made to rotate upon it. When the grinding is completed by the use of this tool...
Then Fredericus addressed unwinged words to Mary Ann: "O thou goddess, what age has brought thee forth? while shadows move round the convex mountains, while heaven feeds the stars, your name and praise I shall sing to whatever clime I may be called, - but I must leave you now, as the confounded swell is ordering up my supper...