Case II. a greater than 80°. 



Step 4. — (Steps 1 to 3 are the same as in Case I). Pi is 

 established along the deep water orthogonal at a distance 

 from Ci equal to half of one of the proportions of / shown 

 on the protractor. In this case R was selected equal to /. 



The Aor for R/J=l and -^ = 0.02 is 1.15°. Thus P2P3, 



etc., can be established by turning 1.15° at each point and 

 progressing a distance Ri, iSo . . . R5, etc., equal to 

 Ji, Ji . . . Ji until a becomes less than 80°. Any other 

 proportion of RjJ can be selected at any time. It is to 

 be remembered that the angle turned at any P carries the 

 orthogonal a distance of MR beyond the point. 



Case III. — Contours are not simple. 



Ste/p 4.. — (Steps 1 to 3 are the same as for Case I.) As 

 a\ and a2 are zero no refraction occurs between didi and 

 dsds'. P3. 1 can be established on the line OjOi' as the limit 

 of no refraction, as. 2 and 03.4 are approximately 90° so 

 P3.2 and P3.4 are drawn in using ff/J = 0.5. At P3.6, con- 

 ditions change and P3.6 is established as though a contour 



existed at P3 5 with a 7 — between it and didi of ^^X 



0.21 = 0.13. 



That is, J — is reduced by a simple proportion to estab- 



i-ia DC 



lish an intermediate contour interval. The diagram then 

 progresses as usual to P4, P5, etc. 



Fisure 18. 



27 



