By use of the telescope clamp, turn the fieaman Arc up 1 , 2, 3, 4 

 divisions, etc., in succession as in the first column and compare the 

 angle indicated on the principal arc, which should correspond with 

 the values given in the second column. These are computed from 

 the well known formula: i sin 2v. 



In work, it occasionally happens that no multiple setting can 

 be found that will throw the middle wire on the rod. In this case, 

 take a half interval, at any convenient position. Let this be 7.5 2 

 =15, or 1500 ft. Now turn the telescope to the nearest indicator 

 and let it be assumed that the lower wire cut the rod at 8.4. The 

 computed middle wire reading will then be 8.4 + 7.5 = 15.9. 

 Proceed as above. 



Note In none of these calculations is (c + f) taken into con- 

 sideration. All computations begin at the anterior focal point and 



114 



