MEASURING A BASE-UNE) 



In all Coast and Geodetic Survey work the accurately fixed and measured base-line is 

 the foundation upon which everything else rests. It is measured by the use of invar tapes, 

 which are almost wholly unaffected by heat or cold. The tape is stretched under a uniform 

 tension, hence the spring balance in the picture. The marks for each tape-length are made 

 in hardwood posts firmly set in the ground (see page 665). 



662 



