For Use as a Telemeter, the gradienter of the E. P. L. 

 joes not differ materially in theory from the stadia except that the 

 constant ( c + f ) is not considered, and the datum point, is at 

 the pivots, D, (see Fig. 12 ) instead of at the anterior focal point, or 

 renter of the instrument. In such an instrument as the one here 

 considered, which must of necessity work close to the horizon, no 

 correction need be made for inclination of sight.* 



Example 



Level the instrument and suppose the horizon reading to be, 6. 73S 

 Turn graduated drum two revolutions to the right or left 



and suppose the second reading to be - 3.126 



Interval, 1:100 - - - 3.612 

 or 361.2 ft. from the pivots of the instrument. 



On the speculation that any number of subdivisions of the 

 drum, (n), are turned and that an arbirary number of feet, (0, are 

 Covered on the rod at the distance id), we have : 

 d : 10.000 :: f :n 



Having a value of 1/100 of 1 '/c , each subdivision of the dm in 

 will encompass 1 ft. on a rod at 10,000 ft. distance. Suppose 117 

 divisions cover 5 ft. on a rod at a certain distance. Substituting in 

 the above equation, we find that d - 426.5 ft. from the pivots. 

 Tables on pp. XXI VandXXV will be found a convenient reference in 

 this connection. Percentage equivalents in degrees and minutes 

 can be obtained by comparing the first and third columns, thus: 

 1.6$ 055', or \% = 34'23". 



In this connection let it be remembered that 34'23 // is equal to 

 the stadia interval of 1:100. If one has no stadia wires in his 

 instrument, let him measure the intercept subtended by this angle 

 on a rod held horizontally and multiply the factor by 100. No 

 constant is to be added in this case. 



*Any Stadia Reduction Table will shoiv that corrections for horizontal 

 distances due to inclination of sight do not become appreciable until the interval 

 between CPM toCP42' reached. The first is equal to 0.756% and the tecond, 

 1.222%. 



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