ON DIFFRACTION SPECTRA IN THE MICROSCOPE. J7 



EXPLANATION OF FIGURES, 

 IN PLATES II. AND III. 



Fig. I. a, i.b, i.c, r.d, i.e, i.f, i.g, i.b, card diaphragms used in 

 the experiments described. 



Fig. 2, group of parallel lines on prepared object glass. 



Fig. 3, 4. Diffraction images seen on looking into the microscope tube, 

 the eye-piece being removed after focussing upon the group of parallel lines, 

 while the slits in card diaphragms, i.a, are turned so as to be situate at right 

 angles to the lines on the object plate. Fig. 3 is the diffraction spectrum of 

 the lines ruled with wide interspaces. Fig. 4, that of the closer ruled lines. 



Fig. 3* and 4.* A diagram representing the respective spectra of the group 

 of ruled parallel lines produced when card diaphragms, i.a, i.b, and i.e, are 

 used. The bracketing shows which spectra belong to each experiment, 

 whilst the whole figure shows the relation to each other of the respective 

 spectra. 



Fig. 5 shows the doubling of the wide ruled lines by the card diaphragm, 

 I.a. The diffraction spectrum thus filling out the interspaces between the 

 actual lines, causes the closely ruled lines to appear now, as if they were 

 drawn continuously through the upper as well as lower part of the field. 



Fig. 6 shows the effect of card diaphragm i.b, in quadrupling the number 

 of lines seen in the upper half of the field and doubling that of the closer ruled 

 group in the lower half. 



Fig. 7 shows the effect of a card diaphragm i.d, as in experiment II. 

 namely, the disappearance of all the lines. The card i.c, causes the dis- 

 appearance of the wide set lines only, the group of close ruled lines remaining 

 unaffected. 



Fig. 8, in experiment III, shows the effect of card diaphragm i.e, in 

 shutting out the group of close ruled lines leaving the wide-set lines still 

 visible as explained in the diagram fig. 9. 



Figs. 10 and 11 represent the crossed groups of lines on the object plate. 

 Fig. ID, lines crossing at 90°. 



