DIFFRACTION EXPERIMENTS 



6 9 



angles to the two diagonals of the squares, just as would arise from 

 sets of lines in the direction of the diagonals, so that if the theory 

 holds good we ought to find, on obstructing all the other spectra and 



FIG. 58. 



f o o o o o x 



o o O o o 



\o o o o o/ 



o CL 



- -- 



FIG. 59. 



allowing only the diagonal ones to pass to the eye-piece, that the 

 vertical and horizontal lines have disappeared, and two new sets of 

 lines at right angles to the diagonals have taken their place. 



FIG. 61. 



On inserting the diaphragm, fig. 60, and replacing the eye-piece, 

 we find, in the place of the old network, the one shown in fig. 61, 



/ 



x x x x x x 



x 



x x x x x 



X X X X X/ 



FIG. 62. 



FIG. 63. 



the squares being, however, smaller in the proportion of 1 : V 2, as 

 they should be in exact accordance with theory. 



An object such as Pleurosigma angulatum, which gives six 



