3. EQUIPMENT AND INSTRUMENTS 



109 



1 



■ .■^i.,:?.^'^a.a.a 



Figure 47. — Edmonston beam holder — disassembled. 



the requirement is sufficient to justify con- 

 struction of them. 



3-141 Ground survey instruments. — In 



addition to the instruments required for hy- 

 drographic surveys, a survey party must have 

 at hand a variety of instruments for accom- 

 plishment of all phases of the assigned com- 

 bined operations project. These may include 

 any or all of the following: 



(a) Theodolites. Second order direction 

 theodolites are used for most work. Repeat- 

 ing theodolites or first order direction in- 

 struments may be needed for some opera- 

 tions. 



(b) Signal lamps for triangulation. 



(c) Level and rod for leveling to tidal 

 bench marks. 



(d) Transit magnetometer for magnetic 

 observations. 



(e) Alidade, planetable, and telemeter rods 

 for planetable traverses, topographic, or 

 graphic control surveys. 



(f) Stereoscopes for field and office work 

 with air photographs. 



(g) Base measuring equipment (tapes, 

 stretchers, etc.) will be furnished only when 

 needed under the terms of the project 

 instructions. 



(h) Large survey vessels should always 

 carry wire drag gear in amounts suflicient 

 to accomplish any necessary investigations 

 (see 5-124). 



The instruments and equipment in the 

 foregoing list are described in other man- 

 uals which also contain detailed instructions 

 for their use. 



3-142 Tide gages. — Tide gages may be 

 divided into two groups — non-registering 

 gages which require the presence of an ob- 

 server to record the height of the tide, and 

 self-registering or automatic tide gages 

 which record the rise and fall of the tide. 

 Both types of gages are fully described in 

 Special Publication No. 196, Manual of Tide 

 Observations. 



The Coast and Geodetic Survey uses two 

 principal kinds of automatic tide gages which 

 record the tide graphically. The standard 



