Phillips, Percy · London : T. C. & E. C. Jack ; New York : Dodge Pub. Co. · leaf 74
eived. The screen is placed at the DIFFRACTION 71 principal focus of the lens, L, so that parallel rayscoming from the grating will be brought to a focus on it.If the screen is the retina, L is the lens of the eye. If aplane wave comes up to the grating in the direction ofthe arrows the wavelets… … Fig. 41. Q, where the difference of path between two successivewavelets is equal to a whole wave-length. DrawingAC perpendicular to the rays going to Q, BC is the differ-ence of path. If we call a the angle between the raysgoing to P and those going to Q, the angle BAC is also BC equal to a and -^…
Light
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