CHAP. VIII.] SEARCHING FOR VIGIAS 217 



carries away close to the kite, it saves loss if a preventer of slack 

 wire, secured to the tail of the kite, be sphced into the main 

 wire about 4 fathoms up it. 



A report being more liable to errors of longitude than of Method of 

 latitude, a greater margin is necessary in that direction. Long ®^^°^- 

 parallel lines east and west are preferable, but the necessity of 

 turning the ship more or less head to wind at every sounding 

 makes it desirable to run the lines with the wind abeam, as 

 this tends to disturb the reckoning least. 



The difficulty of fixing the position at sea to within a couple Doubt as 

 of miles or so adds another element of uncertainty to our search, position, 

 so that it is only by running the lines of soundings closer than 

 would otherwise be needful that we can at length say positively 

 nothing is there. 



A good idea of the current may be obtained from the general Estima- 

 direction of the ship's head whilst sounding, considered with current, 

 reference to the strength and direction of the wind, and it should 

 be allowed for in shaping the course to preserve the parallelism 

 of the lines, but the less frequently the course is altered the 

 better. 



It is convenient to adopt a scale of I inch to the mile where Scale, 

 sea observations are concerned, and to graduate the sheet on 

 Mercator's projection. 



A good position in the morning twilight should be obtained micai'^" 

 by two pairs of stars on bearings perpendicular to each other, Positions, 

 the lines of position of one pair thus cutting those of the other 

 nearly at right angles. 



During the daytime the dead reckoning should be checked by 

 lines of position from observations of the sun about every two 

 hours throughout the day, taken preferably Avhilst a sounding 

 is being obtained and the ship stationary. Evening twilight 

 stars give another position. 



During the night it is the safest plan to steam slowly head to ^1°^^^^^ 

 wind through the area already examined ; the accuracy of the 

 dead reckoning is then preserved better than if Ijdng-to. 



The interval of darkness may occasionally be used to run an 

 additional line of soundings head to wind outside the area 

 examined during the day, and thus add to the ground cleared 

 up. If there is a bright moon and good horizon, positions by 

 stars should be obtained at intervals. 



