Hualapai Wash water level gauge. Party of Emmett Sheridan

Wiredrag diagram. The basic principle is to drag a wire attached to two vessels. If the wire encounters an obstruction it will come taut and form a "V"

Wiredrag - engine and guiding roller. Deck of contract sloop NENA A. ROWLAND. Wiredrag party of N. H. Heck

Wiredrag - arrangement of deck of guide boat. Deck of contract sloop NENA A. ROWLAND. Wiredrag party of N. H. Heck

Wiredrag - plotting table and instruments on guide boat. Deck of contract sloop NENA A. ROWLAND. Wiredrag party of N. H. Heck

Wiredrag - N. H. Heck watching the brake to stop reel. Reel stopped to attach floats and buoys to mark wire location. Deck of contract sloop NENA A. ROWLAND. Wiredrag party of N. H. Heck. Only known photograph of Nicholas Heck in the field

Diagram of obstructions discovered by wiredrag. Wiredrag party of J. H. Hawley

Wiredrag vessels in Massachusetts Bay party. Guide launch pilot; end launch Two Brothers; large tender at buoy. Wiredrag party of J. H. Hawley

Watching the wire coming in. Working in approaches to Boston Harbor. Wiredrag party of N. H. Heck

Stowage of wiredrag equipment. Working in approaches to Boston Harbor. Wiredrag party of N. H. Heck

Guide launch FORTUNA setting out the drag. Working in approaches to Boston Harbor. Wiredrag party of N. H. Heck

Taking up the drag on the EQUATOR. Wiredrag party of J. A. Daniels

Setting out the large buoy. Wiredrag party of J. A. Daniels

Wiredrag problems - buoys on wire crushed by being pulled under by tides. Wiredrag party of J. A. Daniels

Wiredrag problems - removing kelp from the wire.

Setting a floating signal to help navigate wiredrag operations. Wiredrag party of J. H. Hawley

Contract wiredrag launch TWILIGHT. First view without wiredrag gear - second with wiredrag gear installed. Semaphore signalling device installed on second picture

Wiredrag contract launch ROOSEVELT. Drafting table and shelter for plotting sheet installed. Wiredrag party of A. Joachims

Wiredrag problems - buoys crushed by water pressure. Buoys carried under by strong tidal currents in the Race. Wiredrag party of R. P. Strough

End launch STANDARD equipped for wiredrag work. Wiredrag party of R. P. Strough

Setting out the drag from the guide launch PILOT. Wiredrag party of R. P. Strough

Guide launch PILOT showing drag gear. Wiredrag party of R. P. Strough

Setting out the drag and buoys from the guide launch. Note semaphore signaling device on stern. Wiredrag party of J. H. Hawley

Drowned forest discovered by wiredrag on Lake Washington. Pulling up a moderate size tree. Wiredrag party of N. H. Heck

Wiredrag using oar power. Note third boat at distant right. Wiredrag party off of SURVEYOR

Wiredrag hung up on obstruction at buoy no. 4. Note "V" of buoy path characteristic of obstruction discovery. Wiredrag party off of EXPLORER

Newspaper feature on wiredrag in Brooklyn Daily Eagle. Wiredrag party of B. H. Rigg

Drag tester - Mate Franz Okeson on right. Wiredrag party of B. H. Rigg

C&GS Launch 66 - wiredrag tender in Long Island Sound. Mate Franz Okeson facing camera on right

Wiredrag at Mitchell-Jordan Reservoir. Site for seaplane ferrying landing site . Wiredrag party of Max Ricketts

Some tools of the trade - wiredrag at Mitchell-Jordan Reservoir. Sextants for shooting horizontal angles, 3-arm protractor for plotting positions . Wiredrag party of Max Ricketts

Wiredrag operations at Elephant Butte Reservoir for seaplane landing site. Wiredrag party of Max Ricketts

Leadline sounding during wiredrag operations. Wiredrag party of Max Ricketts

Wiredrag gear on the stern of the LESTER JONES.

Buoys crushed from being swept under by tidal currents. Operations on the LESTER JONES

Current meter being deployed. Operations on the LESTER JONES

Wiredrag operations on the LESTER JONES.

Launch wiredrag operations. L to r - guide launch, tender, end launch. Launches off of PATHFINDER

Diagram of wiredrag operations ca. 1980. Basically the same system as devised in the early Twentieth Century

Chain drag operation - hung up on obstruction. Launches off of PEIRCE

Pole signal with tin cone for reflecting sunlight. Constructed by survey crews under direction of Ferdinand Hassler. Sketch by Assistant John Farley - view looking to south across Long Island Sound

Tripod signal with tin cone for reflecting sunlight. At signal West Base, west end of Great Fire Island Base Line. Constructed by survey crews under direction of Ferdinand Hassler. Sketch by Assistant John Farley - view looking to east

Wooden tower within a tower. Outer tower supports personnel - inner tower supports instrument. First devised by Assistant Edmund Blunt to see over marshes in Delaware Bay area

Survey tower with signal pole and tin cone. At west end of Epping Base Line. Survey monument shows below tower. Stakes on graded surface were for aligning base measuring instruments

Signal pole with flag and tin cone for reflecting sunlight. Epping Plains area of Maine

Signal at Stillpond, Maryland. Instrument height of 120 feet - top of signal 275 feet. 39th Parallel Survey. Record signal height from wooden tower

Field sketch of signal pole on tree stump. Sketch by Cephas Sinclair

129 foot wooden tower at Station Tate. Horse and buggy at lower right corner for scale. Triangulation party of A. T. Mosman

Station Tate showing attached signal pole. Top of signal pole is 175 feet above ground. Triangulation party of A. T. Mosman

Station Greene, Indiana. Instrument height is 152 feet above ground. 39th Parallel Survey. Triangulation party of George A. Fairfield