GANNETT.] GEOGRAPHIC TABLES AND FOKMULAS. 285 
Table 27. — Horizontal distances and elevations from stadia readings. 
This is a most generally useful stadia table for rods reading 1 foot to 
the 100 feet and with angles up to 30^. The values of other measures 
than those given in the table are obtained by multiplying the quanti- 
ties under the proper vertical angle by stadia readings in hundreds of 
units. The quantity representing the focal distance is very small and 
is given at the bottom of eacli page for focal lengths between three- 
fourths and li feet and is represented as a constant equal to c. 
For ordinary work it is not necessary to take the latter into account. 
The direct use of the table involves a multiplication for each result 
obtained. 
Exam/pie. — Let rod intercept be 3.25 feet, and the angle of inclina- 
tion be 5*^ 35'. Then the distance on the horizontal would be 
tZ=:325 feet. 
If we accept the focal distance /'+<' 'i« 1.25 feet, we have from the 
tables 
^f = 3.25 feetX 99.054-1.21 = 323.15 feet, 
and 
A=:3.25 feetx 9.68+0.11 = 31.57 feet. 
