4 DREDGING AND HYDROGRAPHIC RECORDS OF 



was D. 4756, occupied during the Alaska cruise of 1905; the last 

 hydrographic station was H. 4848, of the Eastern Pacific cruise of 

 1904-5. The present expedition extends the series, respectively, to 

 D. 5095 and H. 4896. 



The various kinds of apparatus used at each station are recorded 

 in chronological order, each on a separate line, opposite the station 

 number in the column "Apparatus." 



The "Position" of a station is that point occupied by the vessel, 

 as determined by the navigator at the time of beginning the first 

 operation at that station. The position of the subsequent opera- 

 tions under the same station number correspond in a general way 

 to the line as indicated under "Drift." The distance covered by 

 all the operations of a station, however, is usually not greater than 

 the negligible error of observation, except in stations near shore 

 determined by bearings. 



The degree of accuracy with which positions are located is, how- 

 ever, of greater importance in relation to the hydrographic infor- 

 mation obtained, and a description of the methods is necessary 

 to the proper use of this information. A great part of the region 

 traversed is still unsurveyed; and even where surveyed, parts are 

 incorrectly or incompletely charted. Owing to press of work and lack 

 of time, no opportunity" was afforded to correct such errors, and the 

 best available charts were therefore used as the basis of all determina- 

 tions of position when in sight of land; in the column "Chart" is 

 noted the number and edition of the chart used at each station. 

 When in sight of land position was fixed by the method that seemed 

 best in each case — cross bearings, bearing and sextant angle, "three- 

 point problem," vertical sextant angle and compass bearing — and 

 from the position so obtained on the chart in use the latitude and 

 longitude were pricked off and set down in the record as the position 

 of the station. Since in unsurveyed regions different charts of the 

 same locality vary greatly, it is evident that to replot a station 

 accurately in relation to the shore features the position of the station 

 as given by latitude and longitude must be set down on the same 

 chart from ivhich it was determined — that is, the chart specified in the 

 column "Chart." If these charts should hereafter be corrected in 

 latitude and longitude, the positions assigned to the stations must be 

 changed accordingly. 



In conformity with previous practice, an additional position, by 

 true bearing and distance, of some prominent shore feature is given 

 for each station when practicable. As viewed from the sliip, the 

 nearest and most prominent objects on shore from which the ship's 

 position was determined were often topographical features^ incon- 

 spicuous and umiamed on the chart, and impossible of identification 

 by a brief wiitten description. Therefore the bearings given in the 



