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"Professor Swan's Designs.—Among several ingenious arrangements and new forms of agents proposed by Professor Swan is the mode of sending rays from prisms through interstices left between other prisms placed in front, and also a form of agent which he termed the triesoptric prism, in which the rays would undergo two refractions and three reflexions. a are the front and b the triesoptric prisms. The two upper and lower prisms a are constructed of flint glass of high refractive power. It will be observed from the drawing that this ingenious arrangement is nevertheless open to objection, for cones of light of 30 degrees in front and of 65 degrees at the back are lost through the interstices." —The Encyclopedia Britannica, 1910

Swans Designs

"Professor Swan's Designs.—Among several ingenious arrangements and new forms of agents proposed by…