158 



FARM DEVELOPMENT 



Surveying instruments. In planning drainage requir- 

 ing the services of a competent engineer, a number of 

 instruments are needed. These are illustrated in various 

 figures accompanying the text. Notes under the figures 

 describe the instruments and give some instructions as 

 to their use. The farmer needs to know more of the 



Figure 58 shows a 20-inch wye level, such as is used by engineers for rail- 

 road surveying, wagon road surveying and in all drainage surveying where 

 great accuracy is required. The instrument is mounted on a tripod and the 

 operator spreads the legs 3 feet apart, more or less, to bring the telescope even 

 with his eye when slightly stooping. The tripod should be so adjusted that the 

 plate A is in a nearly horizontal position. Turn the telescope so that it rests 

 above two opposite thumb screws, as B, C. With the thumb and forefinger 

 turn these two screws both toward center or both away from center, until the 

 bubble in the spirit level is in the center at D. Now turn the telescope at 

 right angles to its former position so as to be above the other two thumb 

 screws. Turn these screws until the bubble indicates that the telescope is 

 again level. It is wise to turn the instrument the second time over B and C 

 to see that its adjustment is level, and in the course of taking levels the bulb 

 should frequently be inspected and leveled up, especially if the tripod is not 

 firmly placed on solid ground, or if the tripod or the instrument has been in 

 the least jarred out of its position. The use of the set screw at E is to re- 

 strain the telescope from revolving and the alignment screw at F is used to 

 make slight changes in revolving the telescope in line with a leveling rod or 

 with a desired line of stakes upon which levels are to be taken. 



engineer's technique, that he may better understand thf, 

 work and that he may be more liberal in employing the 

 trained engineer when needed. 



The transit is necessary in planning large drainage 

 enterprises. It is used in locating the line and in deter- 

 mining the angles at which branch lines leave the main 

 lines. The use of the transit is not very difficult for one 

 who has a knowledge of algebra, geometry and trigo- 



