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or an approximately parabolic form, by a particular method of giving the 
strokes after the polishing begins to take place. This appears to answer 
the purpose in practice, and corresponds with the anticipation of Newton, 
who suggested that finally we should obtain a method, not mathema- 
tical, but mechanical, of giving the parabolic form to mirrors. From 
what has been said, it will be seen, that the method proposed by Mr. Cecil, 
differs materially from all hitherto proposed. 
