The London, Edinburgh and Dublin philosophical magazine and journal of science . throughthe edge of the screen, and suffers diffraction, and thegeneral agreement between experiment and theory is onlyrendered possible by taking for the latter the rigoroussolution obtained by Sommerfeld, the boundary condition5 = 0 being assumed to be satisfied at the surface of thescreen. Table III. = 30-75 cm. X=4377 0=179°5456. Calculated Intensity of the maxima and minima. Max. 383Min. 018 Max. 4*52Min. 0-02 Max. 338 Min. Max. 0-20 3-200-21 2-450-32 1-170-60 147064 1-
The London, Edinburgh and Dublin philosophical magazine and journal of science . throughthe edge of the screen, and suffers diffraction, and thegeneral agreement between experiment and theory is onlyrendered possible by taking for the latter the rigoroussolution obtained by Sommerfeld, the boundary condition5 = 0 being assumed to be satisfied at the surface of thescreen. Table III. = 30-75 cm. X=4377 0=179°5456. Calculated Intensity of the maxima and minima. Max. 383Min. 018 Max. 4*52Min. 0-02 Max. 338 Min. Max. 0-20 3-200-21 2-450-32 1-170-60 147064 1-39 Calculated distance of the maxima and minima from the edge of the screen in cm. 006 •0140 •020•0278•036•0423 •0490•0558 •060•0(582 •074•079S •082•0912 •092•1014 Observeddistance ofthe minima from theedge of the screen. •0140 •0421?0554 •0681•0796•0907 •1008 60 Problem of Diffraction by a Semi-infinite Screen. The third case investigated is that shown in fig. 3. is asmall positive angle and <£ is nearly equal to In this case practically the whole of the field is dividedequally between the region of shadow and reflexion (markedI. and III. in the figures) and only a comparatively smallportion (marked II. in the figure) is that occupied by theregion of transmission. Both of the dividing boundaries fallwithin the region of the field under observation; and so faras this part of the field is concerned, the approximate theoryof diffraction gives the same result as that found from thecomplete analytical solution satisfying the boundary con-dition 5 = 0. The theoretical form of the illumination curvefrom a typical case of this kind is shown in fig. 2 (a), anda photograph of the diffraction fringes is reproduced inPI. II. fig. 4 (a). Table IV. shows the calculated positionsof the minima of illumination and the experimental datafor comparison. The agreement is satisfactory. Table IV. 3 cm. \ = <£ = !< Calculated widths
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