18 



\ MANUAL FOR NORTHERN WOODSMEN 



wider use, is stadia measurement, or the measurement of 

 distance by wires placed in the focus of a telescope and 

 the space which they cut off on a graduated rod. The 

 principles of this method are stated on page 77. 



For this purpose a light telescope may be fitted to 

 the rear sight of the compass, as shown in the illustra- 



, tion, a level and vertical 

 circle being added if the 

 ^instrument is to be used 

 on rough ground. The 

 cost of such an instrument 

 complete is about the same 

 as that of a compass. Its 

 adjustments will readily 

 be understood from its 

 construction and from 

 consideration of the ad- 

 justments required for the 

 transit. 



The advantages of this 

 instrument in land sur- 

 veying are as follows : 



1. Sights may be taken 

 on steeper ground, either 

 up or down hill, than can 

 be covered through com- 

 pass sights. 



2. Distances over very 

 steep ground can be 

 measured more accurately 

 and quickly than by use 

 of the chain. 



3. Distance across 

 gorges, swamps, and bodies of water can be obtained 

 directly and with ease. 



4. It enables the surveyor himself to perform all the 

 particular work on a survey, and this on short jobs, or 

 wherever reliable chainmen cannot be had, may be a very 

 great advantage. 



Stadia wires in an instrument used for land surveying 



A TELESCOPIC SIGHT 



