THEORY OF MICROSCOPICAL VISION. 23 



should find the image of the upper lines identical with 

 that of the lower. On replacing the eye-piece, we see 

 that it is BO, the upper set of lines are doubled in 

 number, a new line appearing in the centre of the 

 space between each of the old (upper) ones, and upper 

 and lower set having become to all appearance identi- 

 cal, as seen in fig. 7 a. 

 In the same way, if we stop off all but the outer 



^ 



Pio. 8. 



Fia. So. 



spectra, as in fig. 8, the lines are apparently again 

 doubled, as seen in fig. 80. 



A case of apparent creation of structure, similar in 

 principle to the foregoing, though more striking, is 

 afforded by a network of squares, as in fig. 9, 

 having sides parallel to this page, which gives the 



Fio. 9. 



Fio. 



spectra shown in fig. 90, consisting of vertical rows 

 for the horizontal lines and horizontal rows for the 

 vertical ones. But it is readily seen that two diagonal 

 rows of spectra exist at right angles to the two diago- 

 nals 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 



