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PM. Trcms., A, vol. 220, Plate 3. 
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 e 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., XS 2 (3) is seen; also the lines linked to it by - e, - e - n, - e + u, - e -f 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 - - 2e are in the observed region 
and have been seen. 
AS contains several examples of displaced lines. 
