382 



HYDROGRAPHICAL SURVEYING [chap. xmi. 



features of a chart in order to distinguish tliem more clearly 

 than by using black alone : 



Side for 

 Scale. 



Towns and Buildings 



Lakes 



Sand and Shingle 



Hill Contour Lines 



Heights and Stations 



Sandy Islets 



Sand-banks that dry 



Coral 



Roads 



Low-water Rotks 



Mud 



Mangroves . . i 



Cultivated Ground ' 



Grass and Meadow Land j 



Trees . . . . / 



Swampy and Marshy Land 



Current Arrows . . 



One-Fathom Line 



Other Fathom Lines 



Carmine tint. 



Cobalt tint round the edge 



Indian Ink pen- work. 



Faint Indian Ink. 



Carmine. 



Black dots. 



Gamboge dots. 



Carmine and Burnt Sienna. 



Burnt Sienna. 



Burnt Sienna pen-work. 



Payne's Gray, edge of fine black dots. 



Prussian Green pen-work. 



Prussian Blue pen- work. 



Indian Ink, 



Black dots. 



Carmine contour lines. 



The three and five fathom lines should be coloured with cobalt — the former 

 with a light tint all over the space included between it and low water, and 

 the latter with a narrow edge inside the fathom line. 



Too great elaboration in working up sand or mud flats, low- 

 water rocks, and coral, should be avoided, as this is as bad for 

 photographic purposes as a colour wash ; this is especially the 

 case where the low- water line approaches the high line. In 

 the latter case care should be taken to leave a clear space 

 between the low and high water lines. 



Hills are better left unshaded, the topography being repre- 

 sented by contour lines alone, as sho^^^l in Fig. 73. 



The scale of the chart is got from the longest calculated 

 distance on it. This ^\^ll, in cases of plans, generally be the 

 same as that we originally plotted from, in which case we 

 •already know our scale. But if we were obliged to plot from 

 a short side, and have since obtained data which will enable 

 us to calculate a longer distance, we must measure the distance 

 between the two points on our chart, and dividing this number, 

 of inches and decimals by the distance as calculated, we shall 

 get the true scale. 



It is well to indicate the two stations from which the scale 

 is derived, by drawing a red line between them, and "v\Titing, 

 either against it, or elsewhere on the chart, the calculated dis- 

 tance and bearing. If a long distance, this last should be the 

 Mercatorial bearing. 



