The Cordova daily times., 1921-01-06
THIRD INSTALLMENT IMPORTANCE OF WIRE DRAG


 Ordinary Photographic surveys are made with launch or other vessel, which proceeds back and forth across the area to be surveyed until the entire area is covered by a system of sounding lines, usually parallel. The distance between the sounding lines | depends on the depth ad ature of the bottom and the importance of the locality. AS the boat follows these lines the depth of water is obtained by means of lead and line, cast at regular intervals from the boat. Such surveys must be made in all regions | in order that the contour of the bottom beneath the surface of the water may be known; and along the sandy portions of our coast surveys by this method may be sufficient. This is decidedly not the case, how ever, in regions where there are ob- structions of small area, such as pin nacle rocks, powders, and sharp, rocky lodges, for it is only by chance that they can be found by an ordi- ary Photographic survey. It is diff ficult to explain just how elusive these dangers are when sought with analogy, balloon drifting slowly analogy, bolloon drifting slowly over town. Imagine the difficulty of throwing weight attached to a line and hitting the tip of a church spire or the gable of a house as the balloon passes over them, and remem- Der that the Photographer not only 1 can not see the obstruction beneath the surface, but does not even know | that it exists
 It has, therefore, been necessary to supplement ordinary Photographic surveys by some means of finding all l of these dangers in regions where ! they exist, and for this purpose the coast and geodetic survey uses an apparatus known as the wire drag. | Starting on the Atlantic coast in 1904 the survey has gradually de. veloped and perfected equipment and methods of operation until at the present time great need for estab. fishing monuments (survey control points, throughout the territory and determining their latitude, longitude, and elevation.
 (a) Along the coast such control points have been established in many localities where Photographic sur veys have been made, but they are not connected with each other or with the other surveys of the United States or Canada. In the interior along the international boundary and in a few small areas inland, but all these various regions must be con nected in the immediate future to avoid wasted efforts, costly later ad justments, and delay in the de- velOpment of the country.
 There is no place in the territory of the United States where maps are of more value in industries of vari- ous kinds than in the interior of Alaska. These maps, of course, should be good ones, and the only possible way to have a good map is to have properly co-ordinated and consist ent system of control.
 The method of determining the geographic positions of monuments which are used for the control points of the topographic maps and surveys of various kinds of triangulation. In this method a base line or distance between two established points is measured and other distances be- tween contiguous points are deter mined by computations from this known length and the measured angles of the triangles in the scheme of triangulation. The attitudes of these stations are the distances from the equator and the longitures are the distances from the meridian passing through the observatory at Greenwich.
 (b) To join these various detached bits of triangulation and to connect the whole of Alaska to the surveys of the remainder of the continent in it's proper geographic relation, obSerVa- tions have been begun with the CO operation of the Canadian govern ment on a strong chain of triangula tiOn to reach from the vicinity Of