The science of light . (C to ~D in the lower row). Whenthe ball B strikes against C it will not be brought to astandstill as it would if C were equal to it, but willrebound from it and so start a disturbance which willbe transmitted back to A. If the original disturbancebe started at D instead of at A it will travel to C withoutany reflected disturbance, but when C strikes against ^ minium ?*? 1 Is* * Fig. 6. 22 THE SCIENCE OF LIGHT B it will not be brought to a standstill by the smallerball but will follow on after the impact. It will thenswing back and start a disturbance travelling backagai
The science of light . (C to ~D in the lower row). Whenthe ball B strikes against C it will not be brought to astandstill as it would if C were equal to it, but willrebound from it and so start a disturbance which willbe transmitted back to A. If the original disturbancebe started at D instead of at A it will travel to C withoutany reflected disturbance, but when C strikes against ^ minium ?*? 1 Is* * Fig. 6. 22 THE SCIENCE OF LIGHT B it will not be brought to a standstill by the smallerball but will follow on after the impact. It will thenswing back and start a disturbance travelling backagain to D. We may now imagine the two rows ofballs to be two media whose surface of separation is atthe point between B and C. When any disturbanceoriginates in one of the media it is propagated throughit until it reaches the surface of separation. At thispoint two disturbances are produced, one which passeson into the second medium, and the other which is re-flected back into the first. From this point of view \ Fig. 7. therefore each point in the surface of separation isconsidered as a new source of disturbance, and we mayinvestigate the laws of reflection by constructing theHuygens secondary wavelets from these points. Reflection of a Plane Wave by a Plane Surface.—Let us take as our simplest case a plane wave incidenton a plane surface and let Fig. 7 represent the sectionwhich is perpendicular to both the wave and the represents the surface and CD represents the planewave-front moving perpendicular to itself up towardsthe surface. If the surface had not been there it wouldhave travelled in a certain time to the position ED7,but as each point in the wave reaches the surface itstarts a secondary wavelet there. The secondary REFLECTION AND REFRACTION 23 wavelet from C will therefore have travelled a distanceCC which is equal to CE at the time when the originalwave would have reached ED. At the same time thesecondary wavelet from / will have reached h whereJh is
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectlight, bookyear1910
