24 THE MICROSCOPE. 



the other spectra and allowing only the diagonal ones 

 to pass to the eye-piece, that the vertical and horizontal 

 lines have disappeared and are replaced by two new 

 sets of lines at right angles to the diagonals. 



On inserting the diaphragm, fig. 10, and replacing 

 the eye-piece, we find in the place of the old network 

 the one shown in fig. 16, the squares being, however, 



FIG. 10. 



FIG. 10a. 



smaller in the proportion of 1 : \/ 2, as they should be 

 in exact accordance with theory. 



An object such as Pleurosigma angulatum, which 

 gives six diffraction spectra arranged as in fig. 11 

 should, according to theory, show markings in a 

 hexagonal arrangement. For there will be one set of 

 lines at right angles to 6, a, e, another set at right 

 angles to c, a, f, and a third at right angles to g, a, d. 



/X X X XT\ 



x x x x X' 



IX X X X X X 

 \ X X X X 



FIG. 11. 



X XA X X/ 



FIG. lla. 



These three sets of lines will obviously produce tho 

 appearance shown in fig. 110. 



A great variety of appearances may be produced 

 with the same arrangement of spectra. Any two 

 adjacent spectra with the central beam (as b, c, a) 

 will form equilateral triangles and give hexagonal 



