INTRODUCTION. 43 



this universally employed instrument will long 

 secure it a place among the first instruments of 

 navigators ; and the defects it may have, cannot be 

 much lessened, but by more frequently heaving, by 

 oftener measuring the log-line, (duly stretching it), 

 and by the use of sand-glasses going longer than the 

 usual half-minute glasses. The glasses themselves 

 must be compared occasionally with a good chro- 

 nometer, and particularly when they are not such 

 as, by being hermetically sealed, secure the sand 

 from the influence of moisture. The v^arious me- 

 thods of deducing the latitude from astronomical 

 observations are likewise known. On a voyage 

 to the north pole, observations on the large fixed 

 stars, and on the planets during the long twilight, 

 might be particularly advisable. The determin- 

 ation of the latitude by lunar altitudes, may, on 

 account of the uncertainty of the time of the 

 greatest altitude, be sometimes wrong by some 

 minutes, even with a good observation, when the 

 moon is near the equator, and her motion in de- 

 clination consequently considerable. It need not 

 be mentioned, that besides the observation at noon, 

 there cannot be too many observations of the lati- 

 tude, as well for the purpose of determining the 

 currents, as for laying down the coast. On shore 

 it is advisable to take the solar altitudes, as well for 

 determining the time as for the latitude, with the 

 artificial horizon, complete directions for which are 

 found in many works, for instance in " Bohnen- 



