. Carnegie Institution of Washington publication. pplied by an interposed burnerin case of the Nernst lamp. The telescopic lens need not be more than 2 , and cross-hairs are not needed. For measuring dispersion the Fraun-hofer lines B, C, D, E, b, F were used. 5 1 . Equations. — The useful equations for present purposes are given in apreceding report,* and the following cases only need be repeated here. If eis the thickness of glass plate of index of refraction /x for the wave-length X,and if the equation fj. = A-{-B/\2, where A and B are constants, be taken assufficient, (i) /i-i where
. Carnegie Institution of Washington publication. pplied by an interposed burnerin case of the Nernst lamp. The telescopic lens need not be more than 2 , and cross-hairs are not needed. For measuring dispersion the Fraun-hofer lines B, C, D, E, b, F were used. 5 1 . Equations. — The useful equations for present purposes are given in apreceding report,* and the following cases only need be repeated here. If eis the thickness of glass plate of index of refraction /x for the wave-length X,and if the equation fj. = A-{-B/\2, where A and B are constants, be taken assufficient, (i) /i-i where A7V is the displacement of the micrometer at the opaque mirror M orN due to the insertion of the plate normally to the component beam in ques-tion. To determine n, B must be known at least approximately. It may bemeasured in the same adjustment, however, if two Fraunhofer lines are usedfiducially. Let dN be the displacement of micrometer to pass the center of * Carnegie Inst. Wash. Pub. No. 229, 1915, §§ 40, 41, 42. 98 THE INTERFEROMETRY OF. ellipses from wave-lengths X to X. Then if e is the thickness of the half-silvered plate H, and R the angle of refraction within it, (2) If e = o, (3) which may be called the corresponding air displacement. Hence 5N-5Na (4) B= ^ ^ ze Vx7 ~ vv Here 8N=dNa=N-N-(Na-Na)=N-Na-(N-Na) so that the difference of the corresponding positions of micrometer for agiven Fraunhofer line, with and without the plate, are to be found. Themethod is quite accurate, as will be seen below. More than two constantsA and B may be taken, if desirable. To return to equation (i), remembering that is small, it is seen thatthe percentage accuracy of ju— i and A/V are about equal. Now AN, for aplate 5 to 6 mm. thick and ordinary glass, is about cm. This may bemeasured within io~4 cm. or 3 parts in io4 of AN or one or two units in thefourth place of n, the index of refraction of the glass. A much more seriousconsideration is the consistent measurement
Size: 2889px × 865px
Photo credit: © Reading Room 2020 / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1910, bookidcarnegieinst, bookyear1917
