Topographic maps and sketch mapping . Fig. 65.—Spirit Leveling. is used. Several forms of clinometers have been devised bymeans of which the vertical angle can be quite accuratelyand rapidly measured, but the slope board is the simplestdevice available and though clumsy is quite as accurate asmost clinometers. The slope board is shown as part of the toji 0^i?S---^. Fig. 66.—Method of Using Slope Board. sketch case equipment in Fig. 55. It is also illustrated inFig. 66, which shows the method of holding the board in theleft hand while the plumb line is steadied by the right hand,the vertical an
Topographic maps and sketch mapping . Fig. 65.—Spirit Leveling. is used. Several forms of clinometers have been devised bymeans of which the vertical angle can be quite accuratelyand rapidly measured, but the slope board is the simplestdevice available and though clumsy is quite as accurate asmost clinometers. The slope board is shown as part of the toji 0^i?S---^. Fig. 66.—Method of Using Slope Board. sketch case equipment in Fig. 55. It is also illustrated inFig. 66, which shows the method of holding the board in theleft hand while the plumb line is steadied by the right hand,the vertical angle being read on the scale at the lower edgeof the board. MEASUREMENT OF ELEVATIONS 119 When using the slope board it is held at the level of theeye, which is about five feet above the ground. In order tomake the line of sight parallel to the inclined distance andobtain the true vertical angle it is necessary to sight an equaldistance above the point B. In Fig. 67 the observer at Asights at his assistant at B and the line of sight FD is parallelto the inclined distance AB, hence the angle DFE equalsthe vertical angle BAC. The distance, DE, which is obtainedby using the former angle and the horizontal distance AC,equals the true difference in elevation, BC. It is frequentlyinconvenient and it is unnecessary to send an assistant tostand at the point B whic
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Keywords: ., bookcentury1900, bookdecade1920, booksubjectcartogr, bookyear1920
