Popular science monthly . eft, over which the depths arenot absolutely known. Jagged pinnaclesof rock projecting from the bottommay rip open the plates of a passing vessel. The projectmasts of a sunken wreckmay be a menacethe navigator, although not visibleabove the lead may slideoff a precipitousrock and give noindication of thetrue depth. A lineof soundings hasbut one dimension,length. The wire-drag line has twodimensions, lengthand breadth. Forevery mile of distancedragged every dangerin a square mile ofarea is detected withabsolute certaint\. Witii the lead linetheir discovery
Popular science monthly . eft, over which the depths arenot absolutely known. Jagged pinnaclesof rock projecting from the bottommay rip open the plates of a passing vessel. The projectmasts of a sunken wreckmay be a menacethe navigator, although not visibleabove the lead may slideoff a precipitousrock and give noindication of thetrue depth. A lineof soundings hasbut one dimension,length. The wire-drag line has twodimensions, lengthand breadth. Forevery mile of distancedragged every dangerin a square mile ofarea is detected withabsolute certaint\. Witii the lead linetheir discovery is moreor less a chance, andit is difficult and oftenwell nigh iniiiossible,to find a rock or shoalof small extent even when its approxi-mate position is known. The vesselsearching for it is as apt to runagainst the obstruction as to find it bysounding. With the drag such a dangercannot escape. Hence it is the onlymeans of finding all submerged dangersin certain areas. Safety of navigationcan be assured by no other The hoisting and measuringequipment on the towing launch The wire-drag is operated in the fol-lowing manner: A horizontal wire sup-ported at any desired dejjlh in the waterl)y a system of uprights attached tofloats at the surface and held down byweights, is drawn through the water bypower boats. Any rock or shoal pro-jecting from the bottom above theeffective depth at which the drag is setis caught by the wire. Soundings arethen taken over the spot, and its positionis located by angles taken to previously(lelermined i^oints on shore. The sound-ings are afterward plotted and placedupon the charts. In practice the draghas developed into a somewhat compli-cated mechanism, but in emergenciesa simple form of drag ma\ be readilyimprovised. Modified forms of thetlrag have been used for find-and removing mines,id for locating sunkenwrecks and is obviouslyadapted to manysuch uses. The a\-crage costof a wire-dragparty is thirtythousand dollars,based on a seaso
Size: 1331px × 1878px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1870, booksubjectscience, bookyear1872
