364 Forestry Quarterly. 



a. real practical value instead of merely having the appearance of 

 a topographic map. 



The draftsman can locate his contours- on the strip by drawing 

 a profile for each strip and then projecting the contours on the 

 strip as shown in figure 4. This method is simple and easily un- 

 derstood but it has the disadvantage of being a very slow method. 

 The plan here proposed is an adaptation -of a practical method used 

 by Professor H. H. Chapman of the Yale Forest School for locat- 

 ing contours with an Abney. 



Chapman's Method. 



The draftsman has the following data: the angle or per cent 

 ■of slope; and the horizontal distance to which this slope ap- 

 plies. 



Tables can be prepared showing the number of contour in- 

 tervals in a given horizontal distance for each degree or per cent 

 of slope. Thus, on a 15% slope there will be a fifty foot con- 

 tour interval every five chains, approximately. If this slope ap- 

 plies to 18 chains of the strip the draftsman has 3 3-5 contour 

 intervals. Assuming that the base line stake has an elevation 

 of 5810 feet, the first 50 foot contour will be located about four 

 chains from the base stake, the second contour nine chains dis- 

 tant, the third fourteen chains, and there will be a remainder of 

 3-5 of a contour interval to apply to the next degree of slope. 



When sketching contours in the field, and the field man has 

 time to perform these mental calculations, the above method is 

 easily used. In the office where the calculations must be made 

 with speed, a mechanical device will be of value. The profiling 

 rule designed is based upon the same principle as the above 

 method. This scale automatically divides the strip into contour 

 intervals and locates the contour on the strip. This scale can be 

 graduated for either per cents of slope or degrees of slope. 

 The graduations of figure 5 are based on a horizontal scale 

 of 16 inches to the mile. 



For each degree of slope or per cent of slope there is a fixed 

 horizontal distance between contours. By graduating this hori- 

 zontal distance between contours, plotted on a field scale of 16 

 inches to the mile, into drop in feet the rule will show the drop 



*See next article. 



