1 88 FARM DEVELOPMENT 



stake, which is Station 2, and the reading shows 5.02 

 and by subtracting we have 105.32 feet, minus 5.02 equals 

 100.30 feet as the height of Station 2 above the 

 imaginary plan called datum. Again, proceeding to 

 Station 3, the rodman holding the measuring rod re- 

 ports that the disk has been stopped in line with the 

 telescope at 4.60 feet. This measurement, subtracted 

 from the height of the instrument, shows that Station 

 3 is 100.72 feet above datum. Station 4 shows that 

 the line is 5.07 feet below the instrument, or 100.25 feet 

 above datum. Station 5 is found to be 3.10 feet below 

 the instrument, or 102.22 feet above datum. 



Getting the new height of the instrument. As a mat- 

 ter of convenience or of necessity, to see the disk on the 

 measuring rod at a long distance, the instrument is moved 

 forward so as to be nearer the successive points along 

 the line of the proposed drain, the heights of which are 

 to be determined. The operator proceeds several stakes 

 beyond the rodman, who remains at the last stake, the 

 height of which was last measured. When the instru- 

 ment is again set up, it is turned upon the measuring 

 rod standing on the hub, the height of which was last 

 determined with the instrument in its previous position. 

 The rodman moves the disk until in line with the in- 

 strument in its new position. He then finds that the 

 measurement is 8.41 feet. The instrument is now con- 

 siderably higher than in its original position. Since the 

 hub on which this measuring rod is standing is known 

 to be 102.22 feet above the imaginary level datum plane, 

 and the eye at the instrument is on a level 8.41 feet 

 above the hub, the height of the instrument is 

 now 102.22, plus 8.41, or 110.63 feet above datum. With 

 this new height of instrument, it is now practicable to 

 proceed to Station 6 and determine its height above 

 datum. Here the rodman, after moving the disk until 

 told that it is level with the instrument, reports that the 



