The science of light . Fig. 31. from a slit S, Fig. 31, illuminated by a sodium flame isreflected by two mirrors, Mx and M2, which are inclinedvery slightly to one another. The slit is turned so thatit is parallel to the line where the two mirrors meet. D 50 THE SCIENCE OF LIGHT The light reflected from Mx appears to come from SL,the image of S in Mv while the Ught reflected from M2appears to come from S2. Where the two reflectedstreams overlap they will interfere as if coming fromtwo interfering sources, S2 and S2, and so an eye-piece, E,will enable one to observe bands parallel to the origin
The science of light . Fig. 31. from a slit S, Fig. 31, illuminated by a sodium flame isreflected by two mirrors, Mx and M2, which are inclinedvery slightly to one another. The slit is turned so thatit is parallel to the line where the two mirrors meet. D 50 THE SCIENCE OF LIGHT The light reflected from Mx appears to come from SL,the image of S in Mv while the Ught reflected from M2appears to come from S2. Where the two reflectedstreams overlap they will interfere as if coming fromtwo interfering sources, S2 and S2, and so an eye-piece, E,will enable one to observe bands parallel to the originalslit. In order to get good bands the inclination of themirrors must be extremely small so as to get Sx and S2very close together. Fresnels Biprism.—In this arrangement the lightfrom a slit S, Fig. 32, passes through a prism of ex-tremely obtuse angle. The light through the upper half. Fig. 32. of the prism is deflected downwards and thereforeappears to come from a source S2, while the light throughthe lower half is deflected upwards and so appears tocome from Sx. Where the two streams overlap, there-fore (the shaded area), there will be interference, and theposition of the bands will be just as if Sx and S2 weretwo interfering sources. The bands are most easilyreceived in an eye-piece. By measuring, as can verysimply be done, the distance between S1 and S2, thedistance between two consecutive bright bands in theeye-piece, and the distance between the slit and theeye-piece, the wave-length of the light may be cal-culated. This method is not very accurate, since thebright bands are not sharp lines whose distance apartcan be measured with extreme accuracy, but are bands INTERFERENCE 51 with a maximum of brightness in the centre graduallyshading off to darkness at the middle of the dark measurement shows that the wave-length is ex-tremely small, however, bein
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectlight, bookyear1910
