44° 



The National Geographic Magazine 



the coasts of the archipelago materially 

 increase the difficulty of carrying on 

 hydrographic work. 



In connection with the hydrography, 

 tidal observations have been made at 3 1 

 places. At Manila an automatic tide- 

 gauge has been maintained for more 

 than two years. The tide staffs are re- 

 ferred to bench-marks. The tide rec- 

 ords are used in reducing the soundings 

 and in predicting the tides, to be in- 

 cluded in the annual Tide Tables pub- 

 lished in Washington. 



A continuous triangulation has been 

 carried along the northwest coast of 



extend to the southward among the 

 islands. 



Topographic surveys with the plane- 

 table have been carried out in connec- 

 tion with nearly all the other work, 

 usually executed simultaneously with 

 the triangulation, but controlled by the 

 latter. A scale of xtroiro" h as generally 

 been used for harbor work and , jj o 

 for general coast work, though these 

 have been varied as conditions required. 

 The topography has been confined to 

 the shore line and adjacent towns and 

 highways, with the location of eleva- 

 tions visible from the coast. In the 



Triangulation Party Starting Out from Manila 



Luzon from Lingayen Gulf to Cape 

 Bojeador, and this is now being ex- 

 tended eastward along the north coast. 

 This triangulation is for the control of 

 the coast line, and extends from the 

 shore to the first line of hills. It is 

 joined to the various astronomical sta- 

 tions and is sufficiently controlled by 

 base lines and observed azimuths. 

 Nearly all the harbor and other survey 

 work is based on triangulation. and is 

 generally connected with one of the as- 

 tronomical stations, and all the points 

 are marked and described. A triangu- 

 lation has been carried to the entrance 

 of Manila Bay, which it is proposed to 



work along the northwest coast of Luzon 

 native ponies were used by the observ- 

 ers, and bull carts for the transportation 

 of instruments. The work progressed 

 satisfactorily under the conditions there 

 found, which were more favorable than 

 in many other districts. The numer- 

 ous substantial church edifices with 

 which the country is dotted furnish the 

 best of artificial landmarks and are a 

 decided assistance in all parts of the 

 survey work. In some localities few 

 additional signals are necessary for hy- 

 drographic or other work. 



In the office of the Survey in Manila 

 detailed plans for the field parties are 



