Laurence, Lionel · London, School of Optics · leaf 17
d itsfocus F, the latter being at the teeth of the wheel. Another lens U, placedat its principal focal length on the other side of the wheel and in a line withthe mirror, renders the light from F parallel. The beam of light is collectedby a third lens L, situated at a distance (say four miles), and… … Fig. 4. Suppose the light escapes through the first gap while the wheel is turningslowly, then it will, after travelling eight miles, pass through the sameopening and a flickering image is seen. If the speed is greater the secondtooth blocks out the light, but if still greater the light passes…
Optics
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