"Knife-edge" Quotes from Famous Books
 ... is polished enough to reflect some light, it should be tested with the knife-edge test. In a dark room, set the speculum against the wall, and a large lamp, L, Fig. 2, twice the focal length away. Place a large sheet of pasteboard, A, Fig. 2, with a small needle hole opposite the blaze, by the side of the lamp, ...
— The Boy Mechanic: Volume 1 - 700 Things For Boys To Do • Popular Mechanics |
