. Carnegie Institution of Washington publication. d will not, therefore, much outlast theFraunhofer lines, so far as width of slit is concerned. Furthermore, even ifthe slit is narrow and the spectra coordinated, there will be no fringes obtain-able if the superimposed solar spectra are quite unbroken—, without in-cidental furrows in the direction of their length (normal to the Fraunhoferlines). For it is to be noticed that the slit is horizontal, and therefore thereis no observable diffraction—, virtually no slit in the horizontal , however, the spectrum field is interrupt
. Carnegie Institution of Washington publication. d will not, therefore, much outlast theFraunhofer lines, so far as width of slit is concerned. Furthermore, even ifthe slit is narrow and the spectra coordinated, there will be no fringes obtain-able if the superimposed solar spectra are quite unbroken—, without in-cidental furrows in the direction of their length (normal to the Fraunhoferlines). For it is to be noticed that the slit is horizontal, and therefore thereis no observable diffraction—, virtually no slit in the horizontal , however, the spectrum field is interrupted longitudinally by a thin( mm.) wire drawn across the slit (or, much better, by very fine specks ofdust lying incidentally within the slit), then these fine opaque objects willeffectively replace the slit, or act analogously to a slit in the horizontal di-rection. Hence fringes will appear when the path-difference is sufficientlysmall, associated with the geometric shadow of the opaque objects, through-out the length of the spectrum. 42. \ V ~~7 c c > • 4 1 i -U 2T We have here, therefore, a peculiar case of the diffraction of a rod, fromtwo separately controlled half-wave-fronts. The fringes at one extreme ofadjustment of mirror M begin with fine horizontal lines, which on moving Mincline and enlarge until they gain the maximum of size in the vertical direc-tion. After this, on further motion of M in the same direction, they inclinefurther, diminish in size, and finally become horizontal and hair-like move along the horizontal axis with M, subject to the equation de X dn 2cos 5/2 where 8/2 is the angle of incidence at M, X the wave-length, and de/dn thenormal displacement of M per fringe. Within the region of overlapping spectra each longitudinal black line iscovered from end to end with fringes, the strip being about of DiD? widthor more if the line is thinner. A broad black line (thicker wire across slit) 64 THE INTERFEROMETRY OF shows the fringes at
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