product of 27r and the values in column (3). 

 Column (5) is the hyperbolic tangent of the values 

 in column (4). Column (6) gives values of X^ in 

 inches and is obtained by multiplying values 

 in column (5) by 8 inches, the base length of 

 the scale. 



In plotting the scales, the value of ordinate at 

 the right-hand side (where c?/io= 0.5) can be made 

 any convenient values. Scale A was made with 

 a height of 2 inches; whereas, scale B was made 

 only 1 inch. This selection of heights seems 

 suitable for the usual hydrographic charts. 



The equations for determining the time interval, 

 t, between, wave crests or the number of wave 

 lengths, n, between crests are determined as 

 follows: 



If the chart scale is in the form -^- and y repre- 

 sents the ordinate in inches where djLo=Q.b, then 



y ^nL„ 

 12 S 



ys 



n- 



yS 



yS 



12L„ 12(5.127^2) (61.44)^2 



(6) 



The time interval, t, between crests is the 

 distance advanced by the wave divided by the 

 wave velocity; that is, at d/Lo = 0.5 



< = 



nLo nL„ 



or 



Co LJT' 



._ yS 



^nT 



(61.44)r 

 Thus, for scale A (fig. 5), where y = 2 inches 

 (0.0326)5' 



(7) 



(8) 



and 



7i = 



t-- 



rp2 



(0.0326)5' 



For scale B (fig. 5), where y=\ inch 



(0.0163)5 



n = 



and 



rp2 



(0.0163)S 



(9) 

 (10) 



(11) 

 (12) 



45 



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