VI. THOMAS KENNEDY. 



advantageous to have the staff divided to read every two- 

 hundredths of a foot instead of one. 



The plotting of plans. — Where the country is steep it is 

 better to adopt a large scale for the plan, and nothing less 

 than two chains to one inch should be adopted where the 

 contours are to be marked at every ten feet apart. The 

 section can be plotted to the ordinary scale used in New 

 South Wales on preliminary railway surveys — that is four 

 chains to one inch. 



For marking off the contours on the plan, the heights are 

 scaled from the plotted section and the points marked on 

 plan of the traverse line. The cross level is written on 

 the plan where the ground changes, and to divide the cross 

 section into even spaces a device is shown on the diagram. 

 A similar one suitable for the work required should be drawn 

 on clear tracing linen. The use of this diagram was found 

 to greatly facilitate the division of the contours. 



Suppose contour lines are to be marked every 5 feet 

 between the points x and y whose heights are 81 and 107 

 feet above datum. It will be observed that every fifth 

 radial Hue is alternately marked different. Assuming as in 

 example, that the bottom outside line represents 80, the 

 next dotted line represents 85 and so on. Now make the 

 station (.v) coincide with any part of the line (81) that is 

 the one next that standing for 80, then run that line over 

 the point until the line corresponding to 107 coincides with 

 the point (//), always taking care that the line between the 

 points themselves is parallel to the lines a, a, a. Prick 

 through on the thick dotted lines which occur between the 

 stations x and y, and in this case these will give the con- 

 tours for 85, 90, 95, 100, and 105. The diagram should be 

 traced and the dotted lines marked alternately red and 

 blue. 



