Hicks. 



Phil. Trans., A, vol. 220, Plate 3. 



1 2 3 4 5 6 



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EXPLANATION OF DIAGRAM. 



(1) A dot represents a wave-number; a large dot the wave-numbers being sounded for. 



(2) A dot to the side of a line denotes a displaced line. 



(3) A circle round a dot denotes that it is in an unobserved region. 



(4) A x denotes that the wave-number has not been seen. 



(5) The links are represented by vertical lines, the u by lines at 45 degrees above the horizontal, the v by 

 lines at 45 degrees below the horizontal. 



(6) The e link is to be subtracted when drawn down and added when drawn up. The u, v links are to be 

 subtracted when drawn to the left and added when drawn to the right. 



E.g., X2 (3) is seen ; also the lines linked to it by - e, -e-u, -e + u, -e + v; that linked by - 2e is not seen, 

 but by -2e + u is. 



XS 3 (3) is out of the observed region, but the lines linked to it by - e, -e-u, - 2e are in the observed region 

 and have been seen. 



* 



AS contains several examples of displaced lines. 



