THE DETERMINATION OF GEOGRAPHICAL POSITION FOR SCIENTIFIC OBSERVATIONS AT SEA 



The value of scientific observations at sea may be 

 enhanced or diminished according as the determinations 

 of geographical position of the different observations 

 are good or poor. For the best determinations of posi- 

 tion there must exist the closest cooperation between 

 the ship's officers and scientific staff, and this coopera- 

 tion is best attained when each group has a fairly good 

 understanding and appreciation of the problems of the 

 other. Perhaps the best results are obtained when the 

 members of one group participate regularly and rather 

 extensively in the activities of the other. On the Carne- 

 gie this latter arrangement always existed. Two or 



more members of the scientific staff always participat- 

 ed in the navigational work, making the customary astro- 

 nomical observations, computing dead reckoning, and 

 making the necessary adjustments of navigational data 

 in its application to all the scientific observations. The 

 ship's officers, on the other hand, took active part in the 

 scientific work and were thus made aware of the need 

 for effective notes on unusual features of meteorological 

 conditions, ship's operation, or scientific work. The re- 

 sult to both groups was greater appreciation of the de- 

 mands for highest accuracy in all phases of the work. 



On all cruises of the Carnegie the accuracy re- 

 quired in navigation was secured by having three ob- 

 servers--two members of the scientific staff and the 

 first watch officer--make all the astronomical observa- 

 tions. Furthermore, six altitudes of a celestial body 

 were taken, weather permitting, in rapid succession for 

 longitude sights, the computations being based on the 

 mean of the six altitudes. Chronometer corrections 

 were known to tenths of seconds with the aid of the radio 

 and were used to that degree of accuracy, and watch 

 corrections were taken to fifths of seconds. The results 

 of the three independent computations usually ranged 

 over approximately one mile, making the mean proba- 

 bly only a few tenths of a mile in error. Observations 

 of latitude at noon likewise usually ranged over about 

 one mile. 



The accuracy of the dead reckoning was limited by 

 the correctness of assumptions as to drift when hove to, 

 to leeway when sailing, and to current. The judgment of 

 the sailing officers on these details was based not only 

 on their long experience at sea, but on their appreciation 

 of the importance of navigational details in relation to 

 the scientific work, and therefore was accepted for the 

 dead reckoning computations. 



On the Carnegie between ten and twenty geographi- 

 cal positions were required each day for the various 

 scientific observations and the dead reckoning had to be 

 adjusted back over varying intervals, from each of the 

 astronomical observations, for each of the positions. It 

 is believed that the positions as determined were accu- 

 rate to within less than a mile under good sailing and 

 navigating conditions. 



On any future expedition it is possible that echo 

 soundings alone may greatly increase the number of 

 geographical positions to be determined each day, the 

 total becoming perhaps as much as forty and fifty, or 

 more. Some of the observations, among them the mag- 

 netic measurements, will require more accurate posi- 

 tions than others. The program outlined for magnetic 

 measurements on a ship that has been adapted and not 

 specially constructed for the purpose (see second paper 

 of this section) will require star sights to precede the 

 swing for declination observations if the latter are made 

 in the morning, or to follow it the observations are made 

 at sunset. Sun sights will provide the position of the 

 swing for the other magnetic measurements during the 

 day. 



It is not intended here to specify any particular 

 method of navigation or to insist that the scientific 

 staff should participate in that work, but it does seem 

 desirable to emphasize the fact that the determination 

 of positions is, in reality, part of the scientific work 

 and requires more detailed attention than is given to it 

 in ordinary navigation. 



94 



