. Carnegie Institution of Washington publication. 50 THE INTERFEROMETRY OF Table i and fig. 35 show the variation of fringes with the angle of incidence *, equation (5). Hence if the angle of incidence is changed from —5° to+ 5°, be increases to nearly 3 times its first value. This, therefore, accounts for the large discrepancies of be found in the successive data below. To secure in- creased sensitiveness and to make the apparatus less sensitive to slight changes of i, this angle should be about 25°, in which case 8e is about three wave-lengths per fringe. But normal incidence is frequently m
. Carnegie Institution of Washington publication. 50 THE INTERFEROMETRY OF Table i and fig. 35 show the variation of fringes with the angle of incidence *, equation (5). Hence if the angle of incidence is changed from —5° to+ 5°, be increases to nearly 3 times its first value. This, therefore, accounts for the large discrepancies of be found in the successive data below. To secure in- creased sensitiveness and to make the apparatus less sensitive to slight changes of i, this angle should be about 25°, in which case 8e is about three wave-lengths per fringe. But normal incidence is frequently more convenient. Finally, in figure 34, if the angle of incidence is i and the two faces G and G' make an angle a with each other and are initially at a distance e apart, changing successively to e' and e", the points a, b, c, being in the same phase, the two rays D and D' leaving at d, at an angle 6—i, will have a path- difference at d equal to cos 0cos a whence (6) ,-(i — cos (6—i}) cosi cos (6— a) X cost cos (6— a) cos a cos 6 (i —cos (6 — i)) TABLE i.—Wallace gratings. £>= i io3XSe i io3X5c + 19040' OC -5° + I5I -10° 0-443 + 10° -15° +5° -20° ±0° -25° This equation reproduces the preceding equation (5) if a = o and the origi- nal equation (2) if a = i = o. It shows that .a discrepancy or angle between the plates is of minor importance. Hence the change of this angle may be used to bring the sodium lines in coincidence when the gratings differ slightly in their grating constants D. On the other hand, changes of incidence i are of extreme importance. Experiments made with the film grating showed that equation (2) not only fits very badly, but that de per fringe is a fluctuating quantity. Table 2 gives some results obtained by measuring the successive values obtained for 5eXios, corresponding to 10 fringes. Fringes were distinctly seen within 3 cm. of displacement by an ordinary t
Size: 1231px × 2030px
Photo credit: © Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookauthorcarnegie, bookcentury1900, bookdecade1900, bookyear1902
