Popular Science Moiilhlij 



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representing; depths spaced more or less 

 widely apart, according to the depth and 

 nature of the bottom. If the depths are 

 great and the bottom of sand or mud, 

 the lines and soundings are wide apart. 

 If the depths arc not great antl the bot- 

 tom rocky and broken, the soundings 

 are closer together; but there is always a 

 considerable interval between liic lines 

 of soundings and between the individual 

 soundings. The soundings represent 

 only the depth over a space of a few 

 inches where the lead touclied bottom. 

 It is between the scnindings that the 

 danger may lie. 



Thus, in the closest survey, large 

 spaces are left, over which the depths are 

 not absolutely known. Jagged pinnacles 

 of rock projecting from the bottom 

 may rip open the plates of a pass 

 ing vessel. The project' 

 masts of a sunken wreck 

 may be a menace 

 the navigator, al 

 though not visible 

 above the surface. 

 The lead may slide 

 off a precipitous 

 rock and give no 

 indication of the 

 true depth. A line 

 of soundings has 

 but one dimension, 

 length. The wire- 

 drag line has two 

 dimensions, length 

 and breadth. For 

 every mile of distance 

 dragged every danger 

 in a square mile of 

 area is detected with 

 absolute certaint\'. 



Witii the lead line 

 their discovery is more 

 or less a chance, and 

 it is difficult and often 

 well nigh iniiiossible, 

 to find a rock or shoal 

 of small extent even when its approxi- 

 mate position is known. The vessel 

 searching for it is as apt to run 

 against the obstruction as to find it by 

 sounding. With the drag such a danger 

 cannot escape. Hence it is the only 

 means of finding all submerged dangers 

 in certain areas. Safety of navigation 

 can be assured by no other means. 



The hoisting and measuring 

 equipment 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 water 

 l)y a system of uprights attached to 

 floats at the surface and held down by 

 weights, is drawn through the water by 

 power boats. Any rock or shoal pro- 

 jecting from the bottom above the 

 effective depth at which the drag is set 

 is caught by the wire. Soundings are 

 then taken over the spot, and its position 

 is located by angles taken to previously 

 (lelermined i^oints on shore. The sound- 

 ings are afterward plotted and placed 

 upon the charts. In practice the drag 

 has developed into a somewhat compli- 

 cated mechanism, but in emergencies 

 a simple form of drag ma\' be readily 

 improvised. Modified forms of the 

 tlrag have been used for find- 

 and removing mines, 

 id for locating sunken 

 wrecks and buoys. 

 It is obviously 

 adapted to many 

 such uses. 



The a\-crage cost 

 of a w i r e - d r a g 

 party is thirty 

 thousand dollars, 

 based on a season's 

 work of from six to 

 eight months. The 

 cost per day is 

 about two hundred 

 and fift}' dollars. 

 Some idea of the 

 importance to this 

 country of surveys of 

 its coasts may be gained 

 by recalling to mind 

 that the coast line of 

 the United States and 

 Alaska, measured along 

 its general trend, ex- 

 ceeds e!e\cn thousand 

 five h mid red miles in 

 length. To represent 

 the actual shore line which must be 

 surveyed and which includes all the 

 islands, ba\'s, sounds, and rivers in the 

 tidal belt, these figures reach the large 

 total of ninety-one thou.sand miles; and 

 to this must be added the shore line of 

 Forto Rico.Ciuam.Tutuila, the Hawaiian 

 and the Philippine Islands, whose coast 

 line is twehe thousand statute miles. 



