Gilbert light experiments for boys . GILBERT LIGHT EXPERIMENTS 31 Experiment No. 24. Twice theangle. Hold the mirror perpen-dicular to the beam. Is the beamreflected back to the slit? Nowturn the mirror to an angle of 45°to the beam. Is the reflected beamturned through an angle of 90°?That is, is the reflected beamturned through twice the anglethe mirror turns? Try other an-gles. The reflected beam turnsthrough twice the angle becausethe angles of incidence and reflec-tion are equal and each is equalto the angle through which themirror turns, therefore, togetherthey are equal to twice this ang
Gilbert light experiments for boys . GILBERT LIGHT EXPERIMENTS 31 Experiment No. 24. Twice theangle. Hold the mirror perpen-dicular to the beam. Is the beamreflected back to the slit? Nowturn the mirror to an angle of 45°to the beam. Is the reflected beamturned through an angle of 90°?That is, is the reflected beamturned through twice the anglethe mirror turns? Try other an-gles. The reflected beam turnsthrough twice the angle becausethe angles of incidence and reflec-tion are equal and each is equalto the angle through which themirror turns, therefore, togetherthey are equal to twice this Fig. 50. HeliograpMng FUN BY DAY WITH ONE MIRRORExperiment No. 25. The heliograph. Reflect sunlight fromyour window (Fig. 50) to a distant building, and have your friendreflect sunlight from near this building to your window. Now send a message to your friend by the Morse code. Un-cover your mirror for a short time for a dot and for a longertime for a dash. He reads the message on the wall of the build-ing. He replies and you read the message on the inside wall ofyour room. This is the principle of the heliograph used formilitary signaling. Experiment No. 26. Height of any point on a building. Driveone end of a straight stick into the ground and make the stickexactly vertical. Place the mirror B, Fig. 51, beside it flat on theground and adjust until the stick and its image are in a straightline; the mirror is then exactly horizontal. 32 GILBERT BOY ENGINEERING J Fig. 51. You find the height of thewindow by reflection Now if you want to find theheight of the topmost window, forexample,
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